Semiconductor device, semiconductor wafer, memory device, and electronic device

ABSTRACT

An object is to provide a semiconductor device with large memory capacity. The semiconductor device includes first to seventh insulators, a first conductor, and a first semiconductor. The first conductor is positioned on a first top surface of the first insulator and a first bottom surface of the second insulator. The third insulator is positioned in a region including a side surface and a second top surface of the first insulator, a side surface of the first conductor, and a second bottom surface and a side surface of the second insulator. The fourth insulator, the fifth insulator, and the first semiconductor are sequentially stacked on the third insulator. The sixth insulator is in contact with the fifth insulator in a region overlapping the first conductor. The seventh insulator is positioned in a region including the first semiconductor and the sixth insulator.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a semiconductordevice, a semiconductor wafer, a memory device, and an electronicdevice.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of the invention disclosed inthis specification and the like relates to an object, a method, or amanufacturing method. In addition, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Specific examples of the technical field of one embodiment ofthe present invention disclosed in this specification include asemiconductor device, a display device, a liquid crystal display device,a light-emitting device, a power storage device, an imaging device, amemory device, a processor, an electronic device, a method for drivingany of them, a method for manufacturing any of them, a method fortesting any of them, and a system including at least one of them.

2. Description of the Related Art

In recent years, electronic components such as central processing units(CPUs), graphics processing units (GPUs), memory devices, and sensorshave been used in various electronic devices such as personal computers,smart phones, and digital cameras. The electronic components have beenimproved to achieve miniaturization, lower power consumption, and othervarious objectives.

Memory devices with large memory capacity are required because theamount of data handled in the aforementioned electronic devices and thelike has increased. As an example of a way to increase the memorycapacity, Patent Document 1 discloses a three-dimensional NAND memoryelement using a metal oxide for a channel formation region.

PATENT DOCUMENT

-   Patent Document 1: U.S. Pat. No. 9,634,097

SUMMARY OF THE INVENTION

A semiconductor layer used in a three-dimensional NAND memory element isdivided into a channel formation region and a low-resistance region.Particularly when a metal oxide is used for the semiconductor layer, howto form the low-resistance region of the metal oxide is important. In atransistor including a semiconductor layer of a metal oxide, a lowcarrier concentration (sometimes also referred to as intrinsic orsubstantially intrinsic in this specification and the like) regionserves as a channel formation region, and a high carrier concentrationregion serves as a low-resistance region. Accordingly, a challenge infabricating a three-dimensional NAND memory element using a metal oxidefor a semiconductor layer is separate formation of a channel formationregion and a low-resistance region.

An object of one embodiment of the present invention is to provide anovel semiconductor device including a semiconductor layer in which achannel formation region and a low-resistance region are formedseparately. Another object of one embodiment of the present invention isto provide a memory device including the semiconductor device. Anotherobject of one embodiment of the present invention is to provide anelectronic device using the memory device including the semiconductordevice. Another object of one embodiment of the present invention is toprovide a memory device with large data capacity. Another object of oneembodiment of the present invention is to provide a highly reliablememory device.

Note that the objects of one embodiment of the present invention are notlimited to the objects mentioned above. The objects described above donot preclude the existence of other objects. The other objects are theones that are not described above and will be described below. The otherobjects that are not described above will be apparent from and can bederived from the description of the specification, the drawings, and thelike by those skilled in the art. One embodiment of the presentinvention achieves at least one of the above objects and the otherobjects. One embodiment of the present invention does not necessarilyachieve all the above objects and the other objects.

(1) One embodiment of the present invention is a semiconductor deviceincluding first to seventh insulators, a first conductor, and a firstsemiconductor. The first conductor is positioned on a first top surfaceof the first insulator. The first conductor is positioned on a firstbottom surface of the second insulator. The third insulator ispositioned in a region including a side surface of the first insulator,a second top surface of the first insulator, a side surface of the firstconductor, a second bottom surface of the second insulator, and a sidesurface of the second insulator. The fourth insulator is in contact withthe third insulator. The fifth insulator is in contact with the fourthinsulator. The first semiconductor is in contact with the fifthinsulator. The sixth insulator is in contact with the firstsemiconductor in a region overlapping the first conductor with the thirdto fifth insulators positioned between the first semiconductor and thefirst conductor. The seventh insulator is positioned in a regionincluding the first semiconductor in a region overlapping the firstinsulator and in a region overlapping the second insulator, and thesixth insulator.

(2) One embodiment of the present invention is a semiconductor deviceincluding first to seventh insulators, a first conductor, and a firstsemiconductor. The first conductor is positioned on a first top surfaceof the first insulator. The first conductor is positioned on a firstbottom surface of the second insulator. The third insulator ispositioned in a region including a second top surface of the firstinsulator, a side surface of the first conductor, and a second bottomsurface of the second insulator. The fourth insulator is in contact withthe third insulator in a region including a region overlapping the firstconductor, a region overlapping the second top surface of the firstinsulator, and a region overlapping the second bottom surface of thesecond insulator. The fifth insulator is positioned in a regionincluding the fourth insulator, a region overlapping a side surface ofthe first insulator, and a region overlapping a side surface of thesecond insulator. The first semiconductor is in contact with the fifthinsulator. The sixth insulator is in contact with the firstsemiconductor in a region overlapping the first conductor with the thirdto fifth insulators positioned between the first semiconductor and thefirst conductor. The seventh insulator is positioned in a regionincluding the first semiconductor in a region overlapping the firstinsulator and in a region overlapping the second insulator, and thesixth insulator.

(3) One embodiment of the present invention is a semiconductor deviceincluding first to seventh insulators, a first conductor, a firstsemiconductor, and a second semiconductor. The first conductor ispositioned on a first top surface of the first insulator. The firstconductor is positioned on a first bottom surface of the secondinsulator. The second semiconductor is positioned on a side surface ofthe first conductor. The third insulator is positioned in a regionincluding a second top surface of the first insulator, a side surface ofthe second semiconductor, and a second bottom surface of the secondinsulator. The fourth insulator is in contact with the third insulatorin a region including a region overlapping the first conductor, a regionoverlapping the second top surface of the first insulator, and a regionoverlapping the second bottom surface of the second insulator. The fifthinsulator is positioned in a region including the fourth insulator, aregion overlapping the second top surface of the first insulator, and aregion overlapping the second bottom surface of the second insulator.The first semiconductor is positioned in a region including the fifthinsulator, a region overlapping a side surface of the first insulator,and a region overlapping a side surface of the second insulator. Thesixth insulator is in contact with the first semiconductor in a regionoverlapping the first conductor with the second semiconductor and thethird to fifth insulators positioned between the first semiconductor andthe first conductor. The seventh insulator is positioned in a regionincluding the first semiconductor in a region overlapping the firstinsulator and in a region overlapping the second insulator, and thesixth insulator.

(4) One embodiment of the present invention is a semiconductor deviceaccording to any of (1) to (3), in which the fourth insulator has afunction of accumulating charge, and charge included in the firstsemiconductor is accumulated in the fourth insulator by supply of apotential to the first conductor.

(5) One embodiment of the present invention is a semiconductor deviceincluding first to third insulators, fifth to seventh insulators, afirst conductor, a second conductor, and a first semiconductor. Thefirst conductor is positioned on a first top surface of the firstinsulator. The first conductor is positioned on a first bottom surfaceof the second insulator. The third insulator is positioned in a regionincluding a second top surface of the first insulator, a side surface ofthe first conductor, and a second bottom surface of the secondinsulator. The second conductor is in contact with the third insulatorin a region overlapping the first conductor. The fifth insulator ispositioned in a region including the third insulator in a regionoverlapping the second top surface of the first insulator and in aregion overlapping the second bottom surface of the second insulator,and the second conductor. The first semiconductor is positioned in aregion including the fifth insulator, a region overlapping a sidesurface of the first insulator, and a region overlapping a side surfaceof the second insulator. The sixth insulator is in contact with thefirst semiconductor in a region overlapping the first conductor with thethird insulator, the second conductor, and the fifth insulatorpositioned between the first semiconductor and the first conductor. Theseventh insulator is positioned in a region including the firstsemiconductor in a region overlapping the first insulator and in aregion overlapping the second insulator, and the sixth insulator.

(6) One embodiment of the present invention is a semiconductor deviceaccording to (5), in which the second conductor has a function ofaccumulating charge, and charge included in the first semiconductor isaccumulated in the second conductor by supply of a potential to thefirst conductor.

(7) One embodiment of the present invention is a semiconductor deviceaccording to any of (1) to (6), further including a third conductor incontact with the seventh insulator.

(8) One embodiment of the present invention is a semiconductor deviceaccording to any of (1) to (7), in which the first semiconductorincludes a low-resistance region at and around an interface with theseventh insulator, and the first semiconductor includes a channelformation region in a region overlapping the first conductor.

(9) One embodiment of the present invention is a semiconductor deviceaccording to (8), in which the first semiconductor contains a metaloxide, the low-resistance region contains a conductive compound, and theconductive compound contains a component included in the metal oxide anda component included in the seventh insulator.

(10) One embodiment of the present invention is a semiconductor deviceaccording to (8), in which the first semiconductor contains a metaloxide, the low-resistance region contains a conductive compound, and theconductive compound contains a component included in the metal oxide,and a metal element.

(11) One embodiment of the present invention is a semiconductor deviceincluding first to seventh insulators, a first conductor, a secondconductor, a first semiconductor, and a second semiconductor. The firstconductor is positioned on a first top surface of the first insulator.The first conductor is positioned on a first bottom surface of thesecond insulator. The second conductor is positioned on a top surface ofthe second insulator. The second conductor is positioned on a bottomsurface of the third insulator. The fourth insulator is positioned in aregion including a side surface of the first insulator, a second topsurface of the first insulator, a side surface of the first conductor, asecond bottom surface of the second insulator, a side surface of thesecond insulator, a side surface of the second conductor, and a sidesurface of the third insulator. The first semiconductor is in contactwith the fourth insulator. The fifth insulator is in contact with thefirst semiconductor in a region overlapping the first conductor with thefourth insulator positioned between the first semiconductor and thefirst conductor. The sixth insulator is positioned in a region includingthe first semiconductor in a region overlapping the first insulator, ina region overlapping the second insulator, in a region overlapping thesecond conductor, and in a region overlapping the third insulator; andthe fifth insulator. The second semiconductor is in contact with thesixth insulator. The seventh insulator is in contact with the secondsemiconductor.

(12) One embodiment of the present invention is a semiconductor deviceincluding first to seventh insulators, a first conductor, a secondconductor, and first to third semiconductors. The first conductor ispositioned on a first top surface of the first insulator. The firstconductor is positioned on a first bottom surface of the secondinsulator. The second conductor is positioned on a top surface of thesecond insulator. The second conductor is positioned on a bottom surfaceof the third insulator. The third semiconductor is positioned on a sidesurface of the first conductor. The fourth insulator is positioned in aregion including a side surface of the first insulator, a second topsurface of the first insulator, the third semiconductor, a second bottomsurface of the second insulator, a side surface of the second insulator,a side surface of the second conductor, and a side surface of the thirdinsulator. The first semiconductor is in contact with the fourthinsulator. The fifth insulator is in contact with the firstsemiconductor in a region overlapping the first conductor with thefourth insulator and the third semiconductor positioned between thefirst semiconductor and the first conductor. The sixth insulator ispositioned in a region including the first semiconductor in a regionoverlapping the first insulator, in a region overlapping the secondinsulator, in a region overlapping the second conductor, and in a regionoverlapping the third insulator; and the fifth insulator. The secondsemiconductor is in contact with the sixth insulator. The seventhinsulator is in contact with the second semiconductor.

(13) One embodiment of the present invention is a semiconductor deviceaccording to (11) or (12), further including a third conductor incontact with the seventh insulator.

(14) One embodiment of the present invention is a semiconductor deviceaccording to any of (11) to (13), in which the first semiconductorincludes a low-resistance region at and around an interface with thesixth insulator, and the first semiconductor includes a channelformation region in a region overlapping the first conductor.

(15) One embodiment of the present invention is a semiconductor deviceaccording to (14), in which the first semiconductor contains a metaloxide, the low-resistance region contains a conductive compound, and thecompound contains a component included in the metal oxide and acomponent included in the sixth insulator.

(16) One embodiment of the present invention is a semiconductor deviceaccording to (14), in which the first semiconductor contains a metaloxide, the low-resistance region contains a compound, and the compoundcontains a component included in the metal oxide, and a metal element.

(17) One embodiment of the present invention is a semiconductor waferincluding a plurality of semiconductor devices according to any one of(1) to (16) and a region to be subjected to dicing.

(18) One embodiment of the present invention is a memory deviceincluding the semiconductor device according to any one of (1) to (16)and a peripheral circuit.

(19) One embodiment of the present invention is an electronic deviceincluding the memory device according to (18) and a housing.

One embodiment of the present invention can provide a novelsemiconductor device including a semiconductor layer in which a channelformation region and a low-resistance region are formed separately. Oneembodiment of the present invention can provide a memory deviceincluding the semiconductor device. One embodiment of the presentinvention can provide an electronic device using the memory deviceincluding the semiconductor device. One embodiment of the presentinvention can provide a memory device with large data capacity. Oneembodiment of the present invention can provide a highly reliable memorydevice.

Note that the effects of one embodiment of the present invention are notlimited to the effects mentioned above. The effects described above donot preclude the existence of other effects. The other effects are theones that are not described above and will be described below. The othereffects will be apparent from and can be derived from the description ofthe specification, the drawings, and the like by those skilled in theart. One embodiment of the present invention has at least one of theabove effects and the other effects. Accordingly, one embodiment of thepresent invention does not have the above effects in some cases.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are circuit diagrams each illustrating a configurationexample of a semiconductor device;

FIG. 2 is a circuit diagram illustrating a configuration example of asemiconductor device;

FIG. 3 is a circuit diagram illustrating a configuration example of asemiconductor device;

FIGS. 4A and 4B are timing charts showing an operation example of asemiconductor device;

FIGS. 5A and 5B are timing charts showing an operation example of asemiconductor device;

FIGS. 6A to 6C are a schematic view, a top view, and a cross-sectionalview for illustrating a structure example of a semiconductor device;

FIGS. 7A to 7C are a schematic view, a top view, and a cross-sectionalview for illustrating a structure example of a semiconductor device;

FIGS. 8A and 8B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 9A and 9B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 10A and 10B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 11A and 11B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 12A and 12B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIG. 13 is a cross-sectional view illustrating an example ofmanufacturing a semiconductor device;

FIGS. 14A and 14B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 15A and 15B are top views illustrating an example of manufacturinga semiconductor device;

FIG. 16 is a top view illustrating an example of manufacturing asemiconductor device;

FIG. 17 is a cross-sectional view illustrating an example ofmanufacturing a semiconductor device;

FIGS. 18A and 18B are top views illustrating an example of manufacturinga semiconductor device;

FIGS. 19A and 19B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIG. 20 is a cross-sectional view illustrating an example ofmanufacturing a semiconductor device;

FIGS. 21A and 21B are top views illustrating an example of manufacturinga semiconductor device;

FIG. 22 is a cross-sectional view illustrating an example ofmanufacturing a semiconductor device;

FIGS. 23A and 23B are top views illustrating an example of manufacturinga semiconductor device;

FIGS. 24A and 24B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIG. 25 is a cross-sectional view illustrating an example ofmanufacturing a semiconductor device;

FIG. 26 is a top view illustrating an example of manufacturing asemiconductor device;

FIGS. 27A and 27B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 28A and 28B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIG. 29 is a top view illustrating an example of manufacturing asemiconductor device;

FIGS. 30A and 30B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIG. 31 is a top view illustrating an example of manufacturing asemiconductor device;

FIGS. 32A to 32C are circuit diagrams each illustrating a configurationexample of a semiconductor device;

FIG. 33 is a circuit diagram illustrating a configuration example of asemiconductor device;

FIG. 34 is a circuit diagram illustrating a configuration example of asemiconductor device;

FIGS. 35A and 35B are timing charts showing an operation example of asemiconductor device;

FIGS. 36A to 36C are a schematic view, a top view, and a cross-sectionalview for illustrating a structure example of a semiconductor device;

FIGS. 37A to 37C are a schematic view, a top view, and a cross-sectionalview for illustrating a structure example of a semiconductor device;

FIGS. 38A and 38B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 39A and 39B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 40A and 40B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 41A and 41B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 42A and 42B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIG. 43 is a cross-sectional view illustrating an example ofmanufacturing a semiconductor device;

FIGS. 44A to 44C are top views illustrating an example of manufacturinga semiconductor device;

FIGS. 45A and 45B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 46A to 46C are top views illustrating an example of manufacturinga semiconductor device;

FIGS. 47A and 47B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 48A and 48B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 49A to 49C are top views illustrating an example of manufacturinga semiconductor device;

FIG. 50 is a cross-sectional view illustrating an example ofmanufacturing a semiconductor device;

FIGS. 51A to 51C are top views illustrating an example of manufacturinga semiconductor device;

FIGS. 52A and 52B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 53A and 53B are cross-sectional views illustrating an example ofmanufacturing a semiconductor device;

FIGS. 54A to 54C are top views illustrating an example of manufacturinga semiconductor device;

FIG. 55 is a cross-sectional view illustrating a semiconductor device;

FIG. 56 is a cross-sectional view illustrating a semiconductor device;

FIGS. 57A and 57B are cross-sectional views illustrating a semiconductordevice;

FIGS. 58A and 58B are cross-sectional views illustrating a semiconductordevice;

FIG. 59 is a block diagram illustrating an example of a memory device;

FIG. 60A is a flow chart showing an example of manufacturing anelectronic component, FIG. 60B is a perspective view of an electroniccomponent, and FIGS. 60C to 60E show perspective views of semiconductorwafers;

FIGS. 61A to 61C each illustrate an atomic ratio range of a metal oxide;

FIG. 62 is a block diagram of a CPU;

FIGS. 63A to 63E are perspective views illustrating examples ofelectronic devices; and

FIGS. 64A to 64F are perspective views illustrating examples ofelectronic devices.

DETAILED DESCRIPTION OF THE INVENTION

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into an oxideinsulator, an oxide conductor (including a transparent oxide conductor),an oxide semiconductor (also simply referred to as an OS), and the like.For example, a metal oxide used in an active layer of a transistor iscalled an oxide semiconductor in some cases. That is, a metal oxideincluded in a channel formation region of a transistor that has at leastone of an amplifying function, a rectifying function, and a switchingfunction can be referred to as a metal oxide semiconductor or shortly asan OS. An OS FET refers to a transistor containing a metal oxide or anoxide semiconductor.

In this specification and the like, a transistor containing silicon inits channel formation region is sometimes referred to as a Sitransistor.

In this specification and the like, a metal oxide including nitrogen isalso called a metal oxide in some cases. Moreover, a metal oxideincluding nitrogen may be called a metal oxynitride.

Embodiment 1

This embodiment will show a circuit configuration, an operating method,and a manufacturing method of a semiconductor device according to oneembodiment of the disclosed invention. In the following description, forexample, [x,y] refers to an element in the x-th row and in the y-thcolumn, and [z] refers to an element in the z-th row or in the z-thcolumn. Such notations are omitted when there is no need to specify acolumn and a row.

<Circuit Configuration Example 1>

First, a circuit configuration of a NAND memory element that is anexample of a semiconductor device will be described with reference toFIG. 1A. FIG. 1A is a circuit diagram of a one-page NAND memory element.The one-page NAND memory element includes n memory cells MC[1] to MC[n](n is an integer of 1 or more), wirings WL[1] to WL[n] for controllingthe memory cells, a wiring BL, a wiring SL, a transistor STr and atransistor BTr for selecting the page, a wiring SSL for controlling thetransistor STr, and a wiring BSL for controlling the transistor BTr. Thewiring WL functions as a wiring for supplying a potential to a controlgate (sometimes simply referred to as a gate in this specification andthe like) of an after-mentioned cell transistor in the memory cell MC.The wiring SL and the wiring BL each function as a wiring for supplyinga potential to a first terminal and/or a second terminal of the celltransistor in the memory cell MC.

Each of the memory cells MC includes a cell transistor CTr. In general,a cell transistor is a normally-on transistor and includes a controlgate and a charge accumulation layer. The charge accumulation layer ispositioned in a region overlapping a channel formation region with atunnel insulating film therebetween. The control gate is positioned in aregion overlapping the charge accumulation layer with a blocking filmtherebetween. In the cell transistor, a tunnel current occurs when awrite potential is supplied to the control gate and a predeterminedpotential is supplied to a first terminal or a second terminal; hence,electrons are injected from the channel formation region into the chargeaccumulation layer. Thus, the threshold voltage of the cell transistorin which electrons are injected into the charge accumulation layer isincreased. As the charge accumulation layer, an insulator or a conductor(a floating gate) can be used. Note that the detailed operatingprinciple of the semiconductor device in FIG. 1A will be describedlater.

The first terminal of the cell transistor CTr is electrically connectedin series with the second terminal of the cell transistor CTr in theadjacent memory cell MC. That is, in the circuit configuration in FIG.1A, the n cell transistors CTr are electrically connected in series. Thesecond terminal of the cell transistor CTr in the memory cell MC[1] iselectrically connected to a first terminal of the transistor STr. Thefirst terminal of the cell transistor CTr in the memory cell MC[n] iselectrically connected to a first terminal of the transistor BTr. Thecontrol gates of the cell transistors CTr in the memory cells MC[1] toMC[n] are electrically connected to the respective wirings WL[1] toWL[n]. A second terminal of the transistor STr is electrically connectedto the wiring SL. A gate of the transistor STr is electrically connectedto the wiring SSL. A second terminal of the transistor BTr iselectrically connected to the wiring BL. A gate of the transistor BTr iselectrically connected to the wiring BSL.

A channel formation region of the cell transistor CTr preferablycontains silicon or a metal oxide that will be described in Embodiment4. Particularly when the channel formation region contains a metal oxidecontaining at least one of indium, an element M (e.g., aluminum,gallium, yttrium, or tin), and zinc, the metal oxide functions as a widegap semiconductor; thus, the cell transistor containing the metal oxidein its channel formation region has ultralow off-state currentcharacteristics. That is, the leakage current of the cell transistor CTrin the off state can be reduced, so that power consumption of thesemiconductor device in one embodiment of the present invention can bereduced. Moreover, channel formation regions of the transistor STr andthe transistor BTr can also contain the above metal oxide.

Alternatively, the channel formation region of the transistor STr and/orthe transistor BTr can have a composition different from that of thecell transistor CTr. For example, it is possible to use a materialcontaining the aforementioned metal oxide for the channel formationregion of the cell transistor CTr and use a material containing siliconfor the channel formation region of the transistor STr and/or thetransistor BTr.

Note that one embodiment of the present invention is not limited to thesemiconductor device illustrated in FIG. 1A. One embodiment of thepresent invention can have a circuit configuration obtained byappropriately changing the circuit configuration of the semiconductordevice in FIG. 1A. For example, one embodiment of the present inventionmay be a semiconductor device in which the cell transistor CTr has abackgate as illustrated in FIG. 1B. In the semiconductor device of FIG.1B including the components of the semiconductor device shown in FIG.1A, the cell transistors CTr in the memory cells MC[1] to MC[n] areprovided with backgates to which a wiring BGL is electrically connected.Instead of including one wiring BGL electrically connected to thebackgates of the cell transistors CTr in the memory cells MC[1] toMC[n], the semiconductor device in FIG. 1B may include wirings BGL thatare electrically connected to the respective backgates independently tosupply different potentials to the backgates. Note that an operationexample of the semiconductor device in FIG. 1B will be described later.

To further increase the memory capacity of the semiconductor devices inFIGS. 1A and 1B, the memory cells MC shown in FIGS. 1A and 1B arearranged in a matrix. For example, a circuit configuration illustratedin FIG. 2 is obtained when the memory cells MC in FIG. 1A are arrangedin a matrix. Note that in this specification and the like, a NAND memoryelement with multiple pages illustrated in FIG. 2 is referred to as aone-block NAND memory element.

In the semiconductor device illustrated in FIG. 2, the semiconductordevice (the one-page NAND memory element) in FIG. 1A is arranged in mcolumns (m is an integer of 1 or more), and the wiring WL iselectrically connected to and shared between the memory cells MC in thesame row. That is, the semiconductor device in FIG. 2 has a matrix of nrows and m columns and includes memory cells MC[1,1] to MC[n,m].Accordingly, in the semiconductor device in FIG. 2, electricalconnection is established through the wirings WL[1] to WL[n], wiringsBL[1] to BL[m], wirings BSL[1] to BSL[m], wirings SL[1] to SL[m], andwirings SSL[1] to SSL[m]. Specifically, the control gate of the celltransistor CTr in the memory cell MC[j,i] (j is an integer of 1 to n,and i is an integer of 1 to m) is electrically connected to the wiringWL[j]. The wiring SL[i] is electrically connected to the second terminalof the transistor STr[i]. The wiring BL[i] is electrically connected tothe second terminal of the transistor BTr[i].

FIG. 2 only illustrates the memory cell MC[1,1], the memory cellMC[1,i], the memory cell MC[1,m], the memory cell MC[j,1], the memorycell MC[j,i], the memory cell MC[j,m], the memory cell MC[n,1], thememory cell MC[n,i], the memory cell MC[n,m], the wiring WL[1], thewiring WL[j], the wiring WL[n], the wiring BL[1], the wiring BL[i], thewiring BL[m], the wiring BSL[1], the wiring BSL[i], the wiring BSL[m],the wiring SL[1], the wiring SL[i], the wiring SL[m], the wiring SSL[1],the wiring SSL[i], the wiring SSL[m], the cell transistors CTr, thetransistor BTr[1], the transistor BTr[i], the transistor BTr[m], thetransistor STr[1], the transistor STr[i], and the transistor STr[m] andomit the other wirings, elements, symbols, and reference numerals.

In FIG. 3, the semiconductor device in FIG. 1B is arranged in m columns(m is an integer of 1 or more). In the semiconductor device in FIG. 3,all the transistors included in the memory cells MC have a backgate;hence, the semiconductor device in FIG. 3 includes wirings BGL[1] toBGL[m] electrically connected to the corresponding backgates. Note thatthe description of the semiconductor device in FIG. 2 is referred to forthe semiconductor device in FIG. 3.

One embodiment of the present invention is not limited to theconfigurations of the semiconductor devices in FIG. 2 and FIG. 3 inwhich the semiconductor device in FIG. 1A or FIG. 1B is arranged in amatrix. One embodiment of the present invention can have a circuitconfiguration obtained by appropriately changing the circuitconfiguration of the semiconductor device in FIG. 2 or FIG. 3. Forexample, FIG. 2 and FIG. 3 show the wirings BSL[1] to BSL[m] as thewirings for controlling the respective transistors BTr[1] to BTr[m];alternatively, one wiring may be electrically connected to the gates ofthe transistors BTr[1] to BTr[m]. Similarly, as the wiring forcontrolling the transistors STr[1] to STr[m], one wiring instead of thewirings SSL[1] to SSL[m] may be electrically connected to the gates ofthe transistors STr[1] to STr[m].

<Operation Method Example 1>

Next, an example of a method for operating the semiconductor device inFIG. 1A or FIG. 1B will be described with reference to FIGS. 4A and 4Band FIGS. 5A and 5B. Note that in the following description, a low-levelpotential and a high-level potential do not represent any fixedpotentials, and specific potentials may vary depending on wirings. Forexample, a low-level potential and a high-level potential supplied tothe wiring BSL may be different from a low-level potential and ahigh-level potential supplied to the wiring BL.

A potential V_(PGM) enables electron injection into a chargeaccumulation layer of the cell transistor CTr when being supplied to thecontrol gate of the cell transistor CTr. A potential V_(PS) enables thecell transistor CTr to be turned on when being supplied to the controlgate of the cell transistor CTr. The wiring SL is supplied with anappropriate potential.

In this operation method example, the wiring BGL illustrated in FIG. 1Bhas previously been supplied with a potential in a range where the celltransistor CTr operates normally, unless otherwise specified.Accordingly, the operations of the semiconductor devices in FIGS. 1A and1B can be considered the same.

<<Write Operation>>

FIG. 4A is a timing chart showing an operation example for writing datainto the semiconductor device. The timing chart in FIG. 4A shows changesin potential level of the wiring WL[p] (p is an integer of 1 to n), thewiring WL[j] (here, j is an integer of 1 to n except p), the wiring BSL,the wiring SSL, and the wiring BL. Note that the timing chart in FIG. 4Ashows an operation example for writing data into the memory cell MC[p].

Before time T10, a low-level potential is supplied to the wiring BL.

Between time T10 and time T13, a low-level potential is constantlysupplied to the wiring SSL. Thus, the low-level potential is supplied tothe gate of the transistor STr, so that the transistor STr is turnedoff.

Between time T10 and time T11, a high-level potential starts to besupplied to the wiring BSL. Thus, the gate potential of the transistorBTr reaches the high-level potential between time T10 and time T11,whereby the transistor BTr is turned on. When the transistor BTr isturned on, the low-level potential supplied from the wiring BL isapplied to the first terminal of the cell transistor CTr in the memorycell MC[n].

Between time T11 and time T12, the potential V_(PS) starts to besupplied to the wiring WL[j]. Hence, the potential of the control gateof the cell transistor CTr in the memory cell MC[j] reaches thepotential V_(PS) between time T11 and time T12. At this time, the celltransistor CTr in the memory cell MC[n] is turned on because thelow-level potential supplied from the wiring BL is supplied to the firstterminal of the cell transistor CTr in the memory cell MC[n].Consequently, the low-level potential supplied from the wiring BL isapplied to the first terminal of the cell transistor CTr in the memorycell MC[n−1]. In other words, the cell transistor CTr in the memory cellMC[j] is turned on in sequence.

Moreover, between time T11 and time T12, the potential V_(PGM) starts tobe supplied to the wiring WL[p]. Hence, the potential of the controlgate of the cell transistor CTr in the memory cell MC[p] reaches thepotential V_(PGM) between time T11 and time T12. Since the low-levelpotential supplied from the wiring BL is supplied to the first terminalof the cell transistor CTr in the memory cell MC[p] according to theaforementioned operation, electrons are injected into the chargeaccumulation layer from the channel formation region of the celltransistor CTr in the memory cell MC [p]. Thus, data is written into thememory cell MC[p]. Note that the threshold voltage of the celltransistor CTr is increased by electron injection into the chargeaccumulation layer from the channel formation region of the celltransistor CTr in the memory cell MC[p].

The low-level potential supplied from the wiring BL is assumed to besupplied up to the first terminal of the transistor STr by time T12.Between time T12 and time T13, a low-level potential starts to besupplied to the wiring WL[j] and the wiring WL[p], and the potentials ofthe wiring WL[j] and the wiring WL[p] become the low-level potentialbetween time T12 and time T13.

After time T13, a low-level potential starts to be supplied to thewiring BSL. Thus, the gate potential of the transistor BTr becomes thelow-level potential after time T13, so that the transistor BTr is turnedoff. Alternatively, although not shown in the timing chart in FIG. 4A,the transistor BTr can be turned off at that time by setting thepotential of the wiring BL to a high-level potential and not supplying alow-level potential to the wiring BSL.

Through the above operation, data can be written into the semiconductordevice in FIG. 1A or FIG. 1B.

<<Read Operation>>

FIG. 4B is a timing chart showing an operation example for reading datafrom the semiconductor device. The timing chart in FIG. 4B shows changesin potential level of the wiring WL[p], the wiring WL[q] (q is aninteger of 1 to n except p), the wiring WL[j] (here, j is an integer of1 to n except p and q), the wiring BSL, the wiring SSL, and the wiringSL, and also shows a change in the amount of I_(READ) as a currentflowing between the wiring SL and the wiring BL. Note that the timingchart in FIG. 4B shows an operation example for reading data from thememory cell MC[p] and the memory cell MC[q], assuming that electronshave been injected into the charge accumulation layer of the celltransistor CTr in the memory cell MC[p] but not into the chargeaccumulation layer of the cell transistor CTr in the memory cell MC[q].

Before time T20, a low-level potential is supplied to the wiring SL.

Between time T20 and time T21, a high-level potential starts to besupplied to the wiring BSL and the wiring SSL. Thus, the gate potentialsof the transistor BTr and the transistor STr reach the high-levelpotential between time T20 and time T21, whereby the transistor BTr andthe transistor STr are turned on. When the transistor STr is turned on,the low-level potential supplied from the wiring SL is applied to thesecond terminal of the cell transistor CTr in the memory cell MC[1].

Between time T21 and time T22, the potential V_(PS) starts to besupplied to the wiring WL[q] and the wiring WL[j]. Hence, the potentialsof the control gates of the cell transistors CTr in the memory cellMC[q] and the memory cell MC[j] reach the potential V_(PS) between timeT21 and time T22. At this time, when the low-level potential suppliedfrom the wiring SL is supplied to the second terminals of the celltransistors CTr in the memory cell MC[q] and the memory cell MC[j],these cell transistors CTr are turned on.

Meanwhile, between time T21 and time T22, a low-level potential issupplied to the wiring WL[p]. Hence, the potential of the control gateof the cell transistor CTr in the memory cell MC[p] becomes thelow-level potential between time T21 and time T22. The threshold voltageof the cell transistor CTr in the memory cell MC[p] has been increasedbecause of electrons injected into the charge accumulation layer of thecell transistor CTr in the memory cell MC[p]. For these reasons, thecell transistor CTr in the memory cell MC[p] is turned off, and acurrent does not flow between the wiring SL and the wiring BL. In otherwords, measuring the amount of current flowing through the wiring BL atthis time to show a current does not flow between the wiring SL and thewiring BL proves that electrons have been injected into the chargeaccumulation layer of the cell transistor CTr in the memory cell MC[p].

Between time T22 and time T23, a low-level potential starts to besupplied to the wiring WL[p], the wiring WL[q], and the wiring WL[j].Hence, the potentials of the control gates of the cell transistors CTrin the memory cells MC[1] to MC[n] become the low-level potentialbetween time T22 and time T23.

Between time T23 and time T24, the potential V_(PS) starts to besupplied to the wiring WL[j]. Thus, the potential of the control gate ofthe cell transistor CTr in the memory cell MC[j] reaches the potentialV_(PS) between time T23 and time T24. At this time, when the low-levelpotential supplied from the wiring SL is supplied to the first terminalof the cell transistor CTr in the memory cell MC[j], the cell transistorCTr is turned on.

Furthermore, between time T23 and time T24, the potential V_(PS) startsto be supplied to the wiring WL[p]. Thus, the potential of the controlgate of the cell transistor CTr in the memory cell MC[p] reaches thepotential V_(PS) between time T23 and time T24. Note that the thresholdvoltage of the cell transistor CTr in the memory cell MC[p] has beenincreased by electron injection into the charge accumulation layer ofthe cell transistor CTr in the memory cell MC[p]; in this operationexample, it is assumed that the cell transistor CTr is substantiallyturned on because the potential V_(PS) is supplied to the control gateof the cell transistor CTr.

Moreover, between time T23 and time T24, a low-level potential issupplied to the wiring WL[q]. Hence, the potential of the control gateof the cell transistor CTr in the memory cell MC[q] becomes thelow-level potential between time T23 and time T24. Note that the celltransistor CTr in the memory cell MC exhibits normally-oncharacteristics; accordingly, the cell transistor CTr in the memory cellMC[q] is turned on even when the low-level potential is supplied fromthe wiring SL to the first terminal of the cell transistor CTr in thememory cell MC[q].

That is, the cell transistors CTr in the memory cells MC[1] to MC[n] areon, so that a current flows between the source and the drain of each ofthe cell transistors CTr. In other words, measuring the amount ofcurrent flowing through the wiring BL at this time to show a currentflows between the wiring SL and the wiring BL demonstrates thatelectrons have not been injected into the charge accumulation layer ofthe cell transistor CTr in the memory cell MC[q].

Between time T24 and time T25, a low-level potential starts to besupplied to the wiring WL[p], the wiring WL[q], and the wiring WL[j].Thus, the potentials of the control gates of the cell transistors CTr inthe memory cells MC[1] to MC[n] become the low-level potential betweentime T24 and time T25.

After time T25, a low-level potential starts to be supplied to thewiring BSL and the wiring SSL. Thus, the gate potentials of thetransistor BTr and the transistor STr become the low-level potentialbetween time T25 and time T26, whereby the transistor BTr and thetransistor STr are turned off.

That is, to read data from a given memory cell MC, a low-level potentialis supplied to the control gate of the cell transistor CTr in the givenmemory cell MC and a high-level potential is supplied to the controlgates of the cell transistors CTr in the other memory cells MC, and thenthe amount of current flowing between the wiring SL and the wiring BL ismeasured, whereby data retained in the given memory cell MC can be readout.

With the above operations, data can be written into and read from thesemiconductor device in FIG. 1A or FIG. 1B.

<<Erase Operation>>

FIG. 5A is a timing chart showing an operation example for erasing datastored in the semiconductor device. The timing chart in FIG. 5A showschanges in potential level of the wiring WL[j] (here, j is an integer of1 to n), the wiring BSL, the wiring SSL, the wiring BL, and the wiringSL. Note that the erase operation for the NAND memory element isperformed on a page-by-page basis.

Before time T30, a low-level potential is supplied to the wiring BL andthe wiring SL.

Between time T30 and time T33, a low-level potential is constantlysupplied to the wiring WL[j].

Between time T30 and time T31, a high-level potential starts to besupplied to the wiring BSL and the wiring SSL. Thus, the gate potentialsof the transistor BTr and the transistor STr reach the high-levelpotential between time T30 and time T31, whereby the transistor BTr andthe transistor STr are turned on. When the transistor BTr and thetransistor STr are turned on, the low-level potential supplied from thewiring SL is supplied to the second terminal of the cell transistor CTrin the memory cell MC[1], and the low-level potential supplied from thewiring BL is supplied to the first terminal of the cell transistor CTrin the memory cell MC[n].

Between time T31 and time T32, a potential VER starts to be supplied tothe wiring BL and the wiring SL. Note that the potential VER is higherthan the high-level potential flowing through the wiring BL and thewiring SL. Accordingly, between time T31 and time T32, the potentials ofthe channel formation regions of all the cell transistors CTr in thememory cells MC[1] to MC[n] increase; hence, electrons injected into thecharge accumulation layer of each of the cell transistors CTr areextracted and moved to the channel formation region.

Between time T32 and time T33, a low-level potential starts to besupplied to the wiring BL and the wiring SL.

After time T33, a low-level potential starts to be supplied to thewiring BSL and the wiring SSL. Thus, the gate potentials of thetransistor BTr and the transistor STr become the low-level potentialbetween time T33 and time T34, whereby the transistor BTr and thetransistor STr are turned off.

Through the above operation, data can be erased from the semiconductordevice in FIG. 1A or FIG. 1B.

In the semiconductor device in FIG. 1B, the erase operation differentfrom the above can be performed by using the wiring BGL. FIG. 5B showsan example of the operation.

Before time T40, a low-level potential is supplied to the wiring BL andthe wiring SL.

Between time T40 and time T45, a low-level potential is constantlysupplied to the wiring WL[j].

Between time T40 and time T41, a low-level potential starts to besupplied to the wiring BSL and the wiring SSL. Thus, the gate potentialsof the transistor BTr and the transistor STr become the low-levelpotential between time T40 and time T41, whereby the transistor BTr andthe transistor STr are turned off. Consequently, the portion between thefirst terminal of the transistor STr and the first terminal of thetransistor BTr becomes floating.

Moreover, between time T40 and time T41, a potential V_(BGER) starts tobe supplied to the wiring BGL. Note that the potential V_(BGER) isextremely high. The portion between the first terminal of the transistorSTr and the first terminal of the transistor BTr is floating, and thepotential of the wiring BGL becomes V_(BGER) between time T40 and timeT41, whereby the potentials of the channel formation regions of all thecell transistors CTr in the memory cells MC[1] to MC[n] are raised bycapacitive coupling. Thus, electrons injected into the chargeaccumulation layer of each of the cell transistors CTr are extracted andmoved to the channel formation region.

Between time T41 and time T42, a high-level potential starts to besupplied to the wiring BSL and the wiring SSL. Hence, the gatepotentials of the transistor BTr and the transistor STr reach thehigh-level potential between time T41 and time T42, whereby thetransistor BTr and the transistor STr are turned on.

Between time T42 and time T43, a high-level potential starts to besupplied to the wiring BL. Thus, the electrons that are extracted fromthe charge accumulation layer of the cell transistor CTr can flowthrough the wiring BL between time T42 and time T43.

Between time T43 and time T44, a low-level potential starts to besupplied to the wiring BL. Then, at time T44, a low-level potentialstarts to be supplied to the wiring BSL and the wiring SSL. Thus, thegate potentials of the transistor BTr and the transistor STr become thelow-level potential, so that the transistor BTr and the transistor STrare turned off. Finally, after time T45, a low-level potential issupplied to the wiring BGL.

As shown in the above operation, data can be erased from thesemiconductor device in FIG. 1B also by using the wiring BGL.

<Structure Example and Manufacturing Method Example 1>

For easy understanding of the structure of the semiconductor devicehaving the circuit configuration in any of FIGS. 1A and 1B, FIG. 2, andFIG. 3 described above, a method for manufacturing the semiconductordevice will be described below.

FIGS. 6A to 6C show a schematic example of the semiconductor deviceshown in FIG. 2 or FIG. 3. FIG. 6A is a perspective view of thesemiconductor device. FIG. 6B is a top view of FIG. 6A. FIG. 6C is across-sectional view along the dashed-dotted line A1-A2 in FIG. 6B.

The semiconductor device includes a structure body in which the wiringsWL and insulators (regions without a hatching pattern in FIGS. 6A to 6C)are stacked.

An opening is formed in the structure body to penetrate the insulatorsand the wirings WL altogether. To provide the memory cell MC in a regionAR that penetrates the wirings WL, an insulator, a conductor, and asemiconductor are formed in the opening. The conductor functions as asource electrode or a drain electrode of the cell transistor CTr in thememory cell MC. The semiconductor functions as a channel formationregion of the cell transistor CTr. Alternatively, without formation ofthe conductor, a channel formation region and a low-resistance regionmay be formed in the semiconductor and the low-resistance region mayserve as the source electrode or the drain electrode of the celltransistor CTr. The region where the insulator, the conductor, and thesemiconductor are formed in the opening is shown as a region HL in FIGS.6A to 6C. In FIG. 6A, the region HL included inside the structure bodyis indicated by a dashed line. Note that when the transistor included inthe memory cell MC has a backgate, the conductor included in the regionHL may function as the wiring BGL electrically connected to thebackgate.

In other words, FIGS. 6A to 6C illustrate that the semiconductor deviceshown in FIG. 1A or FIG. 1B is formed in a region SD1, and thesemiconductor device shown in FIG. 2 or FIG. 3 is formed in a regionSD2.

A region TM where the wiring WL is exposed functions as a connectionterminal for supplying a potential to the wiring WL. That is, connectinga wiring to the region TM enables a potential to be supplied to the gateof the cell transistor CTr.

Note that the shape of the region TM is not limited to that in thestructure example shown in FIGS. 6A to 6C. The semiconductor device ofone embodiment of the present invention may be configured, for example,such that an insulator is formed over the region TM in FIGS. 6A to 6C,an opening is provided in the insulator, and a conductor PG is formed tofill the opening (FIGS. 7A to 7C). A wiring ER is formed over theconductor PG, whereby the wiring ER and the wiring WL are electricallyconnected to each other. In FIG. 7A, the conductor PG included insidethe structure body is indicated by a dashed line, and the dashed linerepresenting the region HL is omitted.

In the following Manufacturing method example 1, a method for formingthe memory cell MC illustrated in any of FIGS. 1A and 1B, FIG. 2, andFIG. 3 in the region AR will be described.

<<Manufacturing Method Example 1>>

FIGS. 8A to 14B are cross-sectional views for illustrating an example ofmanufacturing the semiconductor device in FIG. 1A, and are specificallycross-sectional views of the cell transistor CTr in the channel lengthdirection. In the cross-sectional views of FIGS. 8A to 14B, somecomponents are not illustrated for simplification.

As illustrated in FIG. 8A, the semiconductor device in FIG. 1A includesan insulator 101A over a substrate (not shown), a conductor 132A overthe insulator 101A, an insulator 101B over the conductor 132A, aconductor 132B over the insulator 101B, and an insulator 101C over theconductor 132B. Note that a stack including these conductors andinsulators (sometimes also including an insulator, a conductor, and thelike other than the above depending on subsequent steps) is hereinafterreferred to as a stack 100.

As the substrate, an insulator substrate, a semiconductor substrate, ora conductor substrate can be used, for example. Examples of theinsulator substrate include a glass substrate, a quartz substrate, asapphire substrate, a stabilized zirconia substrate (e.g., anyttria-stabilized zirconia substrate), and a resin substrate. Examplesof the semiconductor substrate include a semiconductor substrate ofsilicon, germanium, or the like and a compound semiconductor substrateof silicon carbide, silicon germanium, gallium arsenide, indiumphosphide, zinc oxide, or gallium oxide. Another example is a silicon oninsulator (SOI) substrate in which an insulator region is provided inthe above semiconductor substrate. Examples of the conductor substrateinclude a graphite substrate, a metal substrate, an alloy substrate, anda conductive resin substrate. Other examples are a substrate including ametal nitride and a substrate including a metal oxide. Other examplesinclude an insulator substrate provided with a conductor or asemiconductor, a semiconductor substrate provided with a conductor or aninsulator, and a conductor substrate provided with a semiconductor or aninsulator. Alternatively, any of these substrates over which an elementis provided may be used. Examples of the element provided over thesubstrate include a capacitor, a resistor, a switching element, alight-emitting element, and a memory element.

Alternatively, a flexible substrate may be used as the substrate. As amethod for providing a transistor over a flexible substrate, there is amethod in which the transistor is formed over a non-flexible substrateand then the transistor is separated and transferred to the flexiblesubstrate. In that case, a separation layer is preferably providedbetween the non-flexible substrate and the transistor. As the substrate,a sheet, a film, or a foil containing a fiber may be used. The substratemay have elasticity. The substrate may have a property of returning toits original shape when bending or pulling is stopped; alternatively,the substrate may have a property of not returning to its originalshape. The substrate has a region with a thickness of, for example,greater than or equal to 5 μm and less than or equal to 700 μm,preferably greater than or equal to 10 μm and less than or equal to 500μm, more preferably greater than or equal to 15 μm and less than orequal to 300 μm. When the substrate has a small thickness, the weight ofthe semiconductor device including the transistor can be reduced.Moreover, when the substrate has a small thickness, even in the case ofusing glass or the like, the substrate may have elasticity or a propertyof returning to its original shape when bending or pulling is stopped.Thus, an impact applied to the semiconductor device over the substratedue to dropping or the like can be reduced. That is, a robustsemiconductor device can be provided.

For the flexible substrate, a metal, an alloy, a resin, glass, or afiber thereof can be used, for example. The flexible substratepreferably has a lower coefficient of linear expansion, in which casedeformation due to an environment is suppressed. The flexible substrateis formed using, for example, a material with a coefficient of linearexpansion of lower than or equal to 1×10⁻³/K, lower than or equal to5×10⁻⁵/K, or lower than or equal to 1×10⁻⁵/K. Examples of the resininclude polyester, polyolefin, polyamide (e.g., nylon and aramid),polyimide, polycarbonate, and acrylic. In particular, aramid ispreferably used for the flexible substrate because of its lowcoefficient of linear expansion.

In the manufacture example described in this embodiment, heat treatmentis performed in the process; therefore, a material having high heatresistance and a low coefficient of thermal expansion is preferably usedfor the substrate.

The conductor 132A (the conductor 132B) functions as the wiring WL inFIG. 1A.

For the conductors 132A and 132B, a material containing one or moremetal elements selected from aluminum, chromium, copper, silver, gold,platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium,vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium,and ruthenium can be used, for example. Alternatively, a semiconductorhaving high electric conductivity, typified by polycrystalline siliconincluding an impurity element such as phosphorus, or silicide such asnickel silicide may be used.

For the conductors 132A and 132B, a conductive material containingoxygen and a metal element included in a metal oxide usable for asemiconductor 151 (described later) may be used. A conductive materialcontaining the metal element mentioned above and nitrogen may be used.For example, a conductive material containing nitrogen, such as titaniumnitride or tantalum nitride, may be used. As another example, indium tinoxide, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium zinc oxide, or indiumtin oxide to which silicon is added may be used. As another example,indium gallium zinc oxide containing nitrogen may be used. Using such amaterial sometimes allows capture of hydrogen or water entering from aninsulator or the like around the conductor.

For the conductors 132A and 132B, it is preferable to use a conductivematerial having a function of preventing the passage of impurities suchas water or hydrogen. For example, tantalum, tantalum nitride, titanium,titanium nitride, ruthenium, ruthenium oxide, or the like is preferablyused, and a single layer or stacked layers can be used.

A stack including a plurality of conductors formed with any of the abovematerials may be used. For example, it is possible to employ a layeredstructure using a combination of a material including any of the abovemetal elements and a conductive material including oxygen; or a layeredstructure using a combination of a material including any of the abovemetal elements and a conductive material including nitrogen. As anotherexample, it is possible to employ a layered structure using acombination of a material including any of the above metal elements, aconductive material including oxygen, and a conductive materialincluding nitrogen. When an insulator including an excess-oxygen regionis used as the insulator in contact with the conductor, oxygen sometimesdiffuses into a region of the conductor in contact with the insulator,which may result in a layered structure using a combination of amaterial including the metal element and a conductive material includingoxygen. Similarly, when an insulator including an excess-nitrogen regionis used as the insulator in contact with the conductor, nitrogensometimes diffuses into a region of the conductor in contact with theinsulator, which may result in a layered structure using a combinationof a material including the metal element and a conductive materialincluding nitrogen.

The conductors 132A and 132B may be the same material or differentmaterials. That is, materials for the conductors 132A and 132B includedin the semiconductor device of one embodiment of the present inventioncan be selected as appropriate.

There is no particular limitation on a method for forming the conductors132A and 132B. The conductors 132A and 132B can be formed by asputtering method, a CVD method (including a thermal CVD method, anMOCVD method, a PECVD method, or the like), a molecular beam epitaxy(MBE) method, an atomic layer deposition (ALD) method, or a pulsed laserdeposition (PLD) method, for example.

Each of the insulators 101A to 101C is preferably a material with a lowconcentration of impurities such as water or hydrogen, for example. Theamount of hydrogen released from the insulators 101A to 101C, which isconverted into hydrogen molecules per area of one of the insulators 101Ato 101C, is less than or equal to 2×10¹⁵ molecules/cm², preferably lessthan or equal to 1×10¹⁵ molecules/cm², further preferably less than orequal to 5×10¹⁴ molecules/cm² in thermal desorption spectroscopy (TDS)with a temperature of the film surface of the insulator ranging from 50°C. to 500° C., for example. The insulators 101A to 101C may be formedusing an insulator from which oxygen is released by heating.

Each of the insulators 101A to 101C can have a single-layer structure ora layered structure including an insulator containing boron, carbon,nitrogen, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus,chlorine, argon, gallium, germanium, yttrium, zirconium, lanthanum,neodymium, hafnium, or tantalum, for instance. For example, a materialcontaining silicon oxide or silicon oxynitride can be used.

Note that in this specification, silicon oxynitride refers to a materialthat has a higher oxygen content than a nitrogen content, and siliconnitride oxide refers to a material that has a higher nitrogen contentthan an oxygen content. Moreover, in this specification, aluminumoxynitride refers to a material that has a higher oxygen content than anitrogen content, and aluminum nitride oxide refers to a material thathas a higher nitrogen content than an oxygen content.

There is no particular limitation on a method for forming the insulators101A to 101C. The insulators 101A to 101C can be formed by a sputteringmethod, a CVD method (including a thermal CVD method, an MOCVD method, aPECVD method, or the like), an MBE method, an ALD method, or a PLDmethod, for example.

In the next step, as illustrated in FIG. 8B, an opening 191 is formed inthe stack 100 shown in FIG. 8A through resist mask formation and etchingtreatment or the like.

The resist mask can be formed, for example, by a lithography method, aprinting method, or an inkjet method as appropriate. Formation of theresist mask by an inkjet method needs no photomask; thus, manufacturingcost can be reduced. For the etching treatment, either a dry etchingmethod or a wet etching method or both of them may be used.

Then, as illustrated in FIG. 9A, the conductors 132A and 132B positionedon a side surface of the opening 191 are partly removed by etchingtreatment or the like, and a recess portion 192A and a recess portion192B are formed on the side surface. Here, a material for the conductors132A and 132B is selected such that the conductors 132A and 132B areselectively removed in the stack 100 (e.g., a material with a higheretching rate than the insulators 101A to 101C is used).

In the subsequent step, as illustrated in FIG. 9B, an insulator 102 isdeposited in the recess portions 192A and 192B and on the side surfaceof the opening 191 shown in FIG. 9A.

The insulator 102 functions as a gate insulating film of the celltransistor CTr.

For the insulator 102, silicon oxide or silicon oxynitride is preferablyused, for example. Alternatively, for the insulator 102, aluminum oxide,hafnium oxide, or an oxide containing aluminum and hafnium can be used,for example. The insulator 102 may be a stack including any of theabove.

To form the insulator 102, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method (e.g.,a low-pressure CVD (LPCVD) method or a plasma CVD (PCVD) method) mayalternatively be used, for example. As another deposition method, asputtering method can sometimes be used, for instance.

In the next step, as illustrated in FIG. 10A, an insulator 111 isdeposited in the recess portions and on the side surface of the opening191 shown in FIG. 9B. That is, the insulator 111 is formed in contactwith the insulator 102.

A region of the insulator 111 that is overlapped by an after-mentionedregion 151 a of the semiconductor 151 with an after-mentioned insulator104 therebetween functions as the charge accumulation layer of the celltransistor CTr.

For the insulator 111, silicon nitride or silicon nitride oxide ispreferably used, for example.

The description on the method for forming the insulator 102 is referredto for a method for forming the insulator 111.

In the next step, as illustrated in FIG. 10B, an insulator 104 isdeposited in the recess portions and on the side surface of the opening191 shown in FIG. 10A. That is, the insulator 104 is formed in contactwith the insulator 111.

The insulator 104 functions as a tunnel insulating film of the celltransistor CTr.

For the insulator 104, silicon oxide or silicon oxynitride is preferablyused, for example. Alternatively, for the insulator 104, aluminum oxide,hafnium oxide, or an oxide containing aluminum and hafnium may be used,for example. The insulator 104 may be a stack including any of theabove. The insulator 104 is preferably thinner than the insulator 102.When the insulator 104 is thinner than the insulator 102, charge can bemoved by the tunnel effect from the semiconductor 151 (described later)to the insulator 111 through the insulator 104.

The description on the method for forming the insulator 102 is referredto for a method for forming the insulator 104.

Then, as illustrated in FIG. 11A, the semiconductor 151 is deposited inthe recess portions and on the side surface of the opening 191 shown inFIG. 10B. That is, the semiconductor 151 is formed in contact with theinsulator 104.

For the semiconductor 151, a material containing a metal oxide describedin Embodiment 4 can be used, for example. Alternatively, a materialcontaining silicon (preferably polycrystalline silicon) can be used, forinstance.

When the semiconductor 151 contains a metal oxide, an insulatingmaterial having a function of inhibiting the passage of impurities suchas water or hydrogen in addition to oxygen is preferably used for theinsulator 104 in contact with the semiconductor 151. The formation ofsuch an insulator 104 can sometimes prevent impurities such as water orhydrogen from entering the semiconductor 151 through the insulator 104and becoming water by reaction with oxygen included in the semiconductor151. If water is produced in the semiconductor 151, an oxygen vacancymay be formed in the semiconductor 151. When impurities such as hydrogenenter the oxygen vacancy, an electron serving as a carrier may begenerated. Consequently, if the semiconductor 151 has a regioncontaining a large amount of hydrogen, a transistor including the regionin its channel formation region is likely to have normally-oncharacteristics. To prevent this, the insulator 104 is preferably formedusing an insulating material with a function of inhibiting the passageof impurities such as water or hydrogen as well as oxygen.

Next, a step illustrated in FIG. 11B is described.

When a material containing a metal oxide is used for the semiconductor151, treatment for supplying oxygen may be performed on the exposedsurface of the semiconductor 151 positioned on the side surface of theopening 191. In that case, supply treatment 10 illustrated in FIG. 11Bis considered as a step for supplying oxygen. Examples of treatment forsupplying oxygen include plasma treatment using oxygen in a reducedpressure and heat treatment in an oxygen atmosphere. Specifically,plasma treatment using oxygen is preferably performed with an apparatusincluding a power source for generating high-density plasma usingmicrowaves, for instance. Note that the supply treatment 10 describedhere is not necessarily performed in some cases.

Meanwhile, when a material containing silicon is used for thesemiconductor 151, treatment for supplying an impurity may be performedon the exposed surface of the semiconductor 151 positioned on the sidesurface of the opening 191. In that case, the supply treatment 10 inFIG. 11B is considered as a step for supplying an impurity. Note thatheat treatment is preferably performed on the semiconductor deviceduring the supply treatment 10. For example, as the impurity, a p-typeimpurity (acceptor) such as boron, aluminum, or gallium can be used. Asanother example, as the impurity, an n-type impurity (donor) such asphosphorus or arsenic can be used. Note that the supply treatment 10described here is not necessarily performed in some cases.

To form the semiconductor 151, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method mayalternatively be used, for example. As another deposition method, asputtering method, a sol-gel method, an electrophoretic method, or aspray method can sometimes be used, for instance.

In the next step, as illustrated in FIG. 12A, an insulator 109 isdeposited in the recess portions and on the side surface of the opening191 shown in FIG. 11B. That is, the insulator 109 is formed in contactwith the semiconductor 151.

Preferably, a component contained in the insulator 109 is not acomponent that would form a compound with a component contained in thepreviously formed semiconductor 151 at or around the interface betweenthe insulator 109 and the semiconductor 151. If the compound is formed,the compound is preferably an insulator or a compound that does notserve as a carrier in the semiconductor 151.

Silicon oxide can be used for the insulator 109, for example.

The description on the method for forming the insulator 102 is referredto for a method for forming the insulator 109.

In the subsequent step, as illustrated in FIG. 12B, part of theinsulator 109 positioned in the opening 191 is removed by resist maskformation and etching treatment or the like so that only the insulator109 in the recess portions remains. Thus, an insulator 109 a and aninsulator 109 b are formed. Note that at this time, part of thesemiconductor 151 may be removed as long as the insulator 104 is notexposed at the opening 191.

Note that the description of FIG. 8B is referred to for the resist maskformation and the etching treatment.

When a material containing a metal oxide is used for the semiconductor151, treatment for supplying impurities such as hydrogen may beperformed on the side surface of the opening 191. In that case, supplytreatment 11 illustrated in FIG. 13 is considered as a step (treatment)for supplying impurities such as hydrogen. The supply treatment 11 inFIG. 13 is performed on the insulator 109 a, the insulator 109 b, and aregion 151 b of the semiconductor 151. In FIG. 13, a compound 161A (acompound 161B, a compound 161C) is shown as a compound that contains thecomponent of the semiconductor 151 and the impurities supplied by thesupply treatment 11. By this step, the resistance of the region 151 b ofthe semiconductor 151 can be lowered. Note that the supply treatment 11described here is not necessarily performed in some cases.

Meanwhile, when a material containing silicon is used for thesemiconductor 151, treatment for supplying an impurity may be performedon the side surface of the opening 191. In that case, the supplytreatment 11 illustrated in FIG. 13 is considered as a step (treatment)for supplying an impurity. The supply treatment 11 in FIG. 13 isperformed on the insulator 109 a, the insulator 109 b, and the region151 b of the semiconductor 151. Note that heat treatment is preferablyperformed on the stack 100 during the supply treatment 11. As theimpurity, an n-type impurity (donor) such as phosphorus or arsenic canbe used, for example. As another example, as the impurity, a p-typeimpurity (acceptor) such as boron, aluminum, or gallium can be used.Performing this step enables an impurity region 162A (an impurity region162B, an impurity region 162C) to be formed on or around a surface ofthe region 151 b of the semiconductor 151, thereby lowering theresistance of the region 151 b of the semiconductor 151. Note that thesupply treatment 11 described here is not always necessary when theaforementioned supply treatment 10 in FIG. 11B has been performed.

When a material containing one of silicon and a metal oxide is used forthe semiconductor 151, impurities are not supplied to the region 151 aof the semiconductor 151 because the insulators 109 a and 109 b functionas masks for blocking impurities in the region 151 a where theinsulators 109 a and 109 b are formed in contact with the semiconductor151.

In the subsequent step, as illustrated in FIG. 14A, an insulator 105 isdeposited on the side surface of the opening 191 shown in FIG. 13.

When the semiconductor 151 is a material containing a metal oxide, theinsulator 105 preferably contains silicon nitride, for example. When thesemiconductor 151 is in contact with the insulator 105, nitrogen,nitride, and other components included in the insulator 105 may diffuseinto the semiconductor 151. At this time, heat treatment may or may notbe performed on the stack 100. When nitrogen, nitride, and othercomponents in the insulator 105 diffuse into the semiconductor 151, inFIG. 14A, the compound 161A (the compound 161B, the compound 161C) maybe formed in the semiconductor 151 at and around the interface with theinsulator 105 by nitrogen, nitride, and other components diffused fromthe insulator 105. In that case, the resistance of the region 151 b ofthe semiconductor 151 is lowered. In other words, the resistance of theadjacent cell transistors CTr electrically connected to each other cansometimes be lowered.

Meanwhile, when the semiconductor 151 is a material containing silicon,the insulator 105 preferably contains an impurity (an element or an ion)to be diffused into the semiconductor 151, for example. As the impurity,an n-type impurity (donor) such as phosphorus or arsenic can be used,for example. As another example, as the impurity, a p-type impurity(acceptor) such as boron, aluminum, or gallium can be used.

When the semiconductor 151 is in contact with the insulator 105, animpurity (an element or an ion) contained in the insulator 105 maydiffuse into the semiconductor 151. At this time, heat treatment may ormay not be performed on the stack 100. When such an impurity diffusesinto the semiconductor 151, the impurity region 162A (the impurityregion 162B, the impurity region 162C) may be formed in thesemiconductor 151 at or around the interface with the insulator 105, andthe resistance of the region 151 b of the semiconductor 151 may belowered as a result.

The description on the method for forming the insulator 102 is referredto for a method for forming the insulator 105.

FIG. 13 and FIG. 14A each show the step for lowering the resistance ofthe region 151 b of the semiconductor 151. That is, FIG. 13 and FIG. 14Aeach illustrate the step for forming the compound 161A (the compound161B, the compound 161C) or the impurity region 162A (the impurityregion 162B, the impurity region 162C) in the region 151 b of thesemiconductor 151. Therefore, only one of the steps in FIG. 13 and FIG.14A needs to be performed in the process for manufacturing thesemiconductor device; alternatively, both these steps may be performedin some cases.

In the next step, as illustrated in FIG. 14B, an insulator 106 isdeposited on the insulator 105 to fill the remaining opening 191.

For the insulator 106, an insulating material having a function ofinhibiting the passage of impurities such as water and hydrogen and thelike is preferably used, and aluminum oxide can be used, for example.Note that a material usable for the insulator 106 is not limited to theabove. For example, for the insulator 106, any of the materials usablefor the insulators 101A to 101C can be used to form a film with a lowconcentration of impurities such as water and hydrogen.

As another example, for the insulator 106, an insulating material havinga function of inhibiting the passage of oxygen, such as silicon nitride,silicon nitride oxide, silicon oxynitride, aluminum nitride, or aluminumnitride oxide, is preferably used. When the semiconductor 151 contains amaterial containing a metal oxide, the formation of such an insulator106 can sometimes prevent oxygen included in the semiconductor 151 fromreleasing and diffusing into the insulator 106 through the insulator 105and/or the insulator 109 a (the insulator 109 b). Consequently, thereduction in oxygen concentration of the semiconductor 151 can beprevented in some cases.

As another example, for the insulator 106, an insulating material havinga function of passing oxygen is preferably used. For example, theinsulator 106 may be doped with oxygen so that oxygen may diffusethrough the insulator 105 and/or the insulator 109 a (the insulator 109b), whereby oxygen can sometimes be supplied to the semiconductor 151.Thus, the oxygen concentration of the semiconductor 151 can be increasedin some cases.

For the insulator 106, aluminum oxide can be used, for instance. Whenaluminum oxide is deposited by a sputtering method, oxygen is suppliedto the insulator 105 and/or the insulator 109 a (the insulator 109 b).Oxygen supplied to the insulator 105 and/or the insulator 109 a (theinsulator 109 b) is supplied to the semiconductor 151. As a result, theoxygen concentration of the semiconductor 151 can sometimes beincreased.

The description on the method for forming the insulator 102 is referredto for a method for forming the insulator 106.

Note that the conductor 132A (the conductor 132B) functions as the gateelectrode of the cell transistor CTr and the wiring WL illustrated inFIGS. 1A and 1B. That is, the cell transistor CTr is formed in a region181A (a region 181B) in FIG. 14B.

As described above, the semiconductor device illustrated in FIG. 1A canbe manufactured through the steps from FIG. 8A to FIG. 14B.

FIGS. 15A and 15B are top views of the semiconductor device along thedashed-dotted lines B1-B2 and B3-B4, respectively, in FIG. 14B. FIG. 16is a top view of a semiconductor device including a plurality ofopenings 191 as in the structure example shown in FIGS. 6A to 6C. Notethat FIG. 16 shows that the semiconductor device is provided with aplurality of openings 191 in the top view along the dashed-dotted lineB1-B2 in FIG. 14B. Note also that the positions of the openings 191 arenot limited to those shown in FIG. 16 and may be determined freelyduring circuit design.

One embodiment of the present invention is not limited to the structureexample of the semiconductor device illustrated in FIG. 14B. In oneembodiment of the present invention, the structure of the semiconductordevice in FIG. 14B can be changed as appropriate.

For example, in the semiconductor device of one embodiment of thepresent invention, the cell transistor may be provided with a backgate.To provide the cell transistor with a backgate, a conductor 134 insteadof the insulator 106 is deposited in FIG. 14B so as to fill the opening191. Changing the step in this manner enables fabrication of asemiconductor device illustrated in FIG. 17.

Here, the conductor 134 functions as the wiring BGL illustrated in FIG.1B and FIG. 3.

For the conductor 134, any of the materials usable for theaforementioned conductor 132A (conductor 132B) can be used.

To form the conductor 134, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method mayalternatively be used, for example. As another deposition method, asputtering method, a sol-gel method, an electrophoretic method, or aspray method can sometimes be used, for instance.

FIGS. 18A and 18B are top views of the semiconductor device along thedashed-dotted lines B1-B2 and B3-B4 in FIG. 17. Since the semiconductordevice in FIG. 17 includes the conductor 134, the conductor 134 insteadof the insulator 106 in FIGS. 15A and 15B is provided in the top viewsof FIGS. 18A and 18B.

Note that the insulator 105 illustrated in FIG. 17 may be a stackincluding a plurality of insulators, for example, a stack including theinsulator 105 and the insulator 106 mentioned in the description of FIG.14B (not illustrated here).

For example, part of the process for manufacturing the semiconductordevice of one embodiment of the present invention may be changed. FIGS.19A and 19B and FIG. 20 illustrate steps for forming a low-resistanceregion in the region 151 b of the semiconductor 151 in a mannerdifferent from that in FIG. 13. FIG. 19A shows a step for forming aconductor 139 on the side surface of the opening 191 after the step inFIG. 12B. Specifically, the conductor 139 is formed in contact with theinsulator 109 a (the insulator 109 b) and the region 151 b of thesemiconductor 151.

When the semiconductor 151 contains a material containing a metal oxide,the conductor 139 is preferably, for example, a material having afunction of lowering the resistance of the region 151 b, which is partof the semiconductor 151 and in contact with the conductor 139. For theconductor 139, a metal with a resistance of 2.4×10³ [Ω/sq] or less,preferably 1.0×10³ [Ω/sq] or less, a nitride containing a metal element,or an oxide containing a metal element is used. For the conductor 139,it is possible to use, for example, a metal film of aluminum, ruthenium,titanium, tantalum, tungsten, or chromium, a nitride film containing ametal element (e.g., a film of Al—Ti nitride or titanium nitride), or anoxide film containing a metal element (e.g., a film of indium tin oxideor In—Ga—Zn oxide).

When the semiconductor 151 including a material containing a metal oxideis in contact with the conductor 139, the compound 161A (the compound161B, the compound 161C) may be formed from the component of theconductor 139 and the component of the semiconductor 151 by heattreatment, and thus the resistance of the region 151 b of thesemiconductor 151 may be lowered. Note that the resistance of at leastthe semiconductor 151 at and around the interface with the conductor 139should be lowered. The resistance of the region 151 b is loweredprobably because part of oxygen in the semiconductor 151 at or aroundthe interface with the conductor 139 is absorbed into the conductor 139and oxygen vacancies are generated in the semiconductor 151.

In addition to the above, heat treatment may be performed in anatmosphere containing nitrogen while the semiconductor 151 and theconductor 139 are in contact with each other. With the heat treatment,the metal element, which is the component of the conductor 139, may bediffused into the semiconductor 151 or the metal element, which is thecomponent of the semiconductor 151, may be diffused into the conductor139, and the semiconductor 151 and the conductor 139 may form a metalcompound. Note that at this time, the metal element of the semiconductor151 and the metal element of the conductor 139 may be alloyed, in whichcase the metal elements become comparatively stable, leading to a highlyreliable semiconductor device.

Hydrogen included in the semiconductor 151 becomes comparatively stablewhen entering an oxygen vacancy in the region 151 b of the semiconductor151. Hydrogen in an oxygen vacancy in the region 151 a becomescomparatively stable when being released from the oxygen vacancy by heattreatment at 250° C. or higher, diffusing into the region 151 b, andentering an oxygen vacancy in the region 151 b. Accordingly, heattreatment further lowers the resistance of the region 151 b, and highlypurifies the region 151 (reduces impurities such as water and hydrogentherein) and further increases the resistance of the region 151 a.

When the semiconductor 151 is a material containing silicon, it ispreferred, for example, that the conductor 139 be any of the materialsusable for the conductor 132A (the conductor 132B) and also contain animpurity (an element or an ion) to be diffused into the semiconductor151. As the impurity, an n-type impurity (donor) such as phosphorus orarsenic can be used, for example. As another example, as the impurity, ap-type impurity (acceptor) such as boron, aluminum, or gallium can beused. At this time, heat treatment may be performed on the stack 100, asdetermined by circumstances. When the semiconductor 151 is in contactwith the conductor 139 containing the impurity, the impurity is diffusedinto the semiconductor 151 at and around the interface with theconductor 139, and the impurity region 162A (the impurity region 162B,the impurity region 162C) is formed.

When the impurity contained in the conductor 139 is an n-type impurity(donor), an n-type impurity region may be formed in the region 151 b ofthe semiconductor 151 or in the semiconductor 151 around the interfacewith the conductor 139. On the other hand, when the impurity containedin the conductor 139 is a p-type impurity (acceptor), a p-type impurityregion may be formed in the region 151 b of the semiconductor 151 or inthe semiconductor 151 around the interface with the conductor 139.Consequently, carriers may be generated in the region 151 b of thesemiconductor 151 or in the semiconductor 151 around the interface withthe conductor 139, resulting in lower resistance of the region 151 b insome cases.

The conductor 139 may be a material capable of forming a metal silicidewith a combination of silicon contained in the semiconductor 151, suchas nickel, cobalt, molybdenum, tungsten, or titanium. Alternatively, theconductor 139 may be a material with high conductivity, such asaluminum, copper, or silver. Further alternatively, the conductor 139may be a material with high heat resistance, such as titanium,molybdenum, tungsten, or tantalum.

When heat treatment is performed at this time, a metal silicide issometimes formed in the semiconductor 151 around the interface with theconductor 139 from the conductive material of the conductor 139 and thecomponent of the semiconductor 151. The metal silicide formed in thiscase is shown as the compound 161A (the compound 161B, the compound161C) in FIG. 19A. Moreover, the impurity region 162A (the impurityregion 162B, the impurity region 162C) is sometimes formed in thesemiconductor 151 around the interface with the compound 161A (thecompound 161B, the compound 161C).

That is, by the above manufacturing method, the region 151 b of thesemiconductor 151 can be formed as a low-resistance region and theregion 151 a of the semiconductor 151 can be formed as a channelformation region. Note that the region 151 b serving as thelow-resistance region corresponds to the first terminal and/or thesecond terminal of the cell transistor CTr; hence, the electricresistance between the cell transistors, which are electricallyconnected in series with each other, can be lowered by the abovemanufacturing method.

To form the conductor 139, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method mayalternatively be used, for example. As another deposition method, asputtering method, a sol-gel method, an electrophoretic method, or aspray method can sometimes be used, for instance.

In the step in FIG. 19B, the conductor 139 on the side surface of theopening 191 is removed using etching treatment or the like. At thistime, the insulator 109 a (the insulator 109 b) at and around theinterface with the conductor 139 may be partly removed as well.

Then, as shown in the step in FIG. 20, the insulator 106 is deposited soas to fill the remaining opening 191 in FIG. 19B. The semiconductordevice in which the low-resistance region is formed in the region 151 bof the semiconductor 151 can be manufactured through the abovemanufacturing steps, which are different from the step shown in FIG. 13.

FIGS. 21A and 21B are top views of the semiconductor device along thedashed-dotted lines B1-B2 and B3-B4 in FIG. 20. As an example, theformation of the insulator 105 is omitted in the semiconductor device ofFIG. 20; hence, the top views of FIGS. 21A and 21B show a structurewhere the insulator 105 is omitted from FIGS. 15A and 15B.

As another example, when the semiconductor 151 is a material containinga metal oxide in one embodiment of the present invention, thesemiconductor 151 can have a three-layer structure as in a semiconductordevice illustrated in FIG. 22. In the semiconductor device in FIG. 22,the three-layer structure of the semiconductor 151 can be constitutedsuch that a semiconductor 152A, a semiconductor 152B, and asemiconductor 152C are sequentially formed as the semiconductor 151 bythe step shown in FIG. 11A in the process of manufacturing thesemiconductor device in FIG. 1A.

FIGS. 23A and 23B are top views of the semiconductor device along thedashed-dotted lines B1-B2 and B3-B4 in FIG. 22. In the semiconductordevice in FIG. 22, the semiconductor layer has a three-layer structureobtained by sequential deposition of the semiconductors 152A, 152B, and152C from the outer side (the side closer to the insulator 104);therefore, the top views in FIGS. 23A and 23B show that thesemiconductor 151 in FIGS. 15A and 15B employs the three-layerstructure.

Preferably, the semiconductor 152A is provided in contact with theinsulator 104, and the semiconductor 152C is provided in contact withthe insulator 105 and the insulator 109 a. At this time, for thesemiconductors 152A and 152C, an oxide with a relatively wide energy gapcompared to that of the semiconductor 152B is preferably used. Here, anoxide with a wide energy gap and an oxide with a narrow energy gap aresometimes referred to as a wide gap oxide and a narrow gap oxide,respectively.

When a narrow gap oxide is used for the semiconductors 152A and 152C anda wide gap oxide is used for the semiconductor 152B, the conduction bandminimum energy of the semiconductors 152A and 152C is preferably higherthan that of the semiconductor 152B. That is, the electron affinity ofthe semiconductors 152A and 152C is preferably less than that of thesemiconductor 152B.

For the semiconductors 152A to 152C, a combination of materialscontaining metal elements with different atomic ratios is preferablyused. Specifically, the atomic ratio of the element M to the otherconstituent elements in the metal oxide used for the semiconductors 152Aand 152C is preferably higher than that in the metal oxide used for thesemiconductor 152B. Moreover, the atomic ratio of the element M to In inthe metal oxide used for the semiconductors 152A and 152C is preferablyhigher than that in the metal oxide used for the semiconductor 152B.Furthermore, the atomic ratio of In to the element M in the metal oxideused for the semiconductor 152B is preferably higher than that in themetal oxide used for the semiconductors 152A and 152C.

For the semiconductors 152A and 152C, a metal oxide with a compositionof or close to In:Ga:Zn=1:3:4, 1:3:2, or 1:1:1 can be used, for example.For the semiconductor 152B, a metal oxide with a composition of or closeto In:Ga:Zn=4:2:3 to 4:2:4.1, 1:1:1, or 5:1:6 can be used, for example.Such metal oxides for the semiconductors 152A to 152C are preferablyused in combination to satisfy the above relation of the atomic ratios.For example, it is preferred that a metal oxide with a composition of orclose to In:Ga:Zn=1:3:4 be used for the semiconductors 152A and 152C anda metal oxide with a composition of or close to In:Ga:Zn=4:2:3 to4:2:4.1 be used for the semiconductor 152B. Here, the term “composition”refers to the atomic ratio of an oxide formed over a substrate or theatomic ratio of a sputtering target.

In addition, a CAAC-OS is preferably used for the semiconductors 152Aand 152C; the CAAC-OS will be described in Embodiment 4. When theCAAC-OS is used for the semiconductors 152A and 152C, the c-axis ispreferably aligned perpendicularly to the top surfaces of thesemiconductors 152A and 152C in FIG. 22.

Here, the conduction band minimum energy varies gradually at a junctionportion of the semiconductor 152A (the semiconductor 152C) and thesemiconductor 152B. In other words, the conduction band minimum at thejunction portion of the semiconductor 152A (the semiconductor 152C) andthe semiconductor 152B varies continuously or is continuously connected.To vary the energy level gradually, the density of defect states in amixed layer formed at an interface between the semiconductor 152A (thesemiconductor 152C) and the semiconductor 152B is preferably made low.

Specifically, when the semiconductor 152A (the semiconductor 152C) andthe semiconductor 152B contain the same element (as a main component) inaddition to oxygen, a mixed layer with a low density of defect statescan be formed. For example, when the semiconductor 152B is an In—Ga—Znoxide, it is preferable to use an In—Ga—Zn oxide, a Ga—Zn oxide, galliumoxide, or the like for the semiconductor 152A (the semiconductor 152C),in which case the density of defect states at the interface between thesemiconductor 152A (the semiconductor 152C) and the semiconductor 152Bcan be reduced. Thus, the influence of interface scattering on carrierconduction is small, and the cell transistor can have a high on-statecurrent in some cases.

In the semiconductor device of FIG. 22, the semiconductor 151 in FIG.14B has the three-layer structure; alternatively, the semiconductor mayhave a two-layer structure or a structure including four or more layers.

In the semiconductor device of FIG. 14B, the insulator 111 is positionedon the entire insulator 102 as an example; alternatively, in oneembodiment of the present invention, the insulator 111 can be dividedinto the charge accumulation layers included in each of the celltransistors CTr. FIG. 24A illustrates a step of removing the insulator111 in the opening 191 by resist mask formation and etching treatment orthe like after the step in FIG. 10A so that the insulator 111 remainsonly on the insulator 102 in the recess portions 192A and 192B. Thus, aninsulator 111 a and an insulator 111 b are formed in contact with theinsulator 102 positioned in the recess portion 192A and the recessportion 192B, respectively. Alternatively, in the step of removing theinsulator 111 in the opening 191, the insulator 102 positioned in theopening 191 may also be removed so that the insulator 101A (theinsulator 101B, the insulator 101C) is exposed as illustrated in FIG.24B. Subsequent to the step in FIG. 24A, steps similar to those in FIGS.10B to 14B are performed, thereby constituting a semiconductor deviceillustrated in FIG. 25.

FIG. 26 is a top view of the semiconductor device along thedashed-dotted line B3-B4 in FIG. 25. In the semiconductor device in FIG.25, the insulator 111 in a region that overlaps the insulator 101A (theinsulator 101B, the insulator 101C) with the insulator 102 therebetweenhas been removed; hence, the top view of FIG. 26 shows a structurewithout the insulator 111 between the insulator 102 and the insulator104 in the top view of FIG. 15B. Note that a top view along thedashed-dotted line B1-B2 in FIG. 25 is approximately the same as that inFIG. 15A in some cases.

As another example, in one embodiment of the present invention, thestructure of the gate electrode of the cell transistor CTr may bechanged from that in FIG. 14B in order to improve the reliability of thecell transistor CTr. FIGS. 27A and 27B and FIGS. 28A and 28B illustratean example of a method for manufacturing such a semiconductor device.

In a step illustrated in FIG. 27A, the conductors 132A and 132Bpositioned on the side surface of the opening 191 are partly removed byetching treatment or the like in FIG. 8B, and a recess portion 196A anda recess portion 196B are formed on the side surface. Note that therecess portions 196A and 196B may be formed deeper than the recessportions 192A and 192B shown in FIG. 9A.

In the subsequent step in FIG. 27B, a semiconductor 153 is deposited onthe side surface of the opening 191 and in the recess portions 196A and196B in FIG. 27A.

For the semiconductor 153, a material containing a metal oxide describedin Embodiment 4 is used, for example. Note that a material usable forthe semiconductor 153 is not limited to the above. For example, amaterial other than a metal oxide can be used for the semiconductor 153in some cases. Alternatively, the semiconductor 153 can sometimes bereplaced with a conductor or an insulator, for instance.

To form the semiconductor 153, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method mayalternatively be used, for example. As another deposition method, asputtering method, a sol-gel method, an electrophoretic method, or aspray method can sometimes be used, for instance.

In the next step, as illustrated in FIG. 28A, part of the remainingsemiconductor 153 in the recess portions 196A and 196B and thesemiconductor 153 positioned on the side surface of the opening 191 areremoved by resist mask formation and etching treatment or the like sothat the semiconductor 153 remains in part of the recess portions 196Aand 196B. Thus, a semiconductor 153 a and a semiconductor 153 b areformed.

Subsequently, steps similar to those in FIGS. 9B to 14B are performed,thereby constituting a semiconductor device illustrated in FIG. 28B.

FIG. 29 is a top view of the semiconductor device along thedashed-dotted line B1-B2 in FIG. 28B. In the semiconductor device inFIG. 28B, the semiconductor 153 a (the semiconductor 153 b) is includedbetween the conductor 132A (the conductor 132B) and the insulator 102 inthe region 151 a, which is different from the semiconductor device inFIG. 14B. Accordingly, the top view in FIG. 29 shows a structure wherethe semiconductor 153 b is included between the conductor 132B and theinsulator 102. Note that a top view along the dashed-dotted line B3-B4in FIG. 28B is approximately the same as that in FIG. 15B in some cases.

Since the semiconductor 153 a (the semiconductor 153 b) is in contactwith the insulator 102, impurities such as hydrogen and water includedin the insulator 102 are sometimes diffused into the semiconductor 153 a(the semiconductor 153 b), or impurities such as hydrogen and waterincluded in a region where the insulator 111 and the insulator 104overlap are sometimes diffused into the semiconductor 153 a (thesemiconductor 153 b) through the insulator 102. Since the semiconductor153 a (the semiconductor 153 b) is in contact with the conductor 132A(the conductor 132B), impurities such as hydrogen and water included inthe conductor 132A (the conductor 132B) are sometimes diffused into thesemiconductor 153 a (the semiconductor 153 b). That is, thesemiconductor 153 a (the semiconductor 153 b) has a function ofcapturing impurities such as hydrogen and water. Thus, the resistance ofthe semiconductor 153 a (the semiconductor 153 b) is lowered, and thesemiconductor 153 a (the semiconductor 153 b) can function as the gateelectrode of the cell transistor CTr. In other words, in thesemiconductor device of FIG. 28B, the semiconductor 153 a (thesemiconductor 153 b) captures surrounding impurities such as hydrogenand water, whereby the reliability of the cell transistor CTr can beincreased.

As another example, in one embodiment of the present invention, aconductor may be provided instead of the insulator 111 used for thecharge accumulation layer. FIGS. 30A and 30B illustrate an example of amethod for manufacturing such a semiconductor device. FIG. 30A showsthat a conductor 138 a and a conductor 138 b are formed in part of therecess portion 192A and part of the recess portion 192B, respectively,in FIG. 9B. The conductors 138 a and 138 b are formed as follows: aconductive material to be the conductors 138 a and 138 b is deposited inthe opening 191 and the recess portions 192A and 192B and then isremoved by resist mask formation and etching treatment or the like sothat the conductor 138 a and the conductor 138 b remain in part of therecess portion 192A and part of the recess portion 192B, respectively.After that, steps from the step of depositing the insulator 104 in FIG.10B to the step of depositing the insulator 106 in FIG. 14B aresimilarly performed, thereby constituting the semiconductor device shownin FIG. 30B.

To form the conductors 138 a and 138 b, a deposition method achievinghigh step coverage is preferably employed. As the deposition methodachieving high step coverage, an ALD method is preferably used, and aCVD method may alternatively be used, for example. As another depositionmethod, a sputtering method, a sol-gel method, an electrophoreticmethod, or a spray method can sometimes be used, for instance.

FIG. 31 is a top view of the semiconductor device along thedashed-dotted line B1-B2 in FIG. 30B. In the semiconductor device ofFIG. 30B, the conductor 138 a (the conductor 138 b) is included betweenthe insulator 102 and the insulator 104 in a region overlapping theregion 151 a of the semiconductor 151; hence, the top view in FIG. 31shows a structure including the conductor 138 b between the insulator102 and the insulator 104. Note that a top view along the dashed-dottedline B3-B4 in FIG. 30B is approximately the same as that in FIG. 26 insome cases.

For the conductors 138 a and 138 b, any of the materials usable for theconductor 132A (the conductor 132B) can be used, for example. Note thata material usable for the conductors 138 a and 138 b is not limited tothe above. The conductors 138 a and 138 b can sometimes be replaced withan insulator, a semiconductor, or the like.

<Circuit Configuration Example 2>

Next, a configuration of a semiconductor device that is different fromthe semiconductor devices shown in Circuit configuration example 1 willbe described with reference to FIG. 32A. FIG. 32A is a circuit diagramof n memory cells (n is an integer of 1 or more). Specifically, thecircuit illustrated in FIG. 32A includes the memory cells MC[1] to MC[n]and wirings WWL[1] to WWL[n], wirings RWL[1] to RWL[n], a wiring WBL,and a wiring RBL for controlling the memory cells. The wiring WWLfunctions as a write word line, the wiring RWL functions as a read wordline, the wiring WBL functions as a write bit line, and the wiring RBLfunctions as a read bit line.

Each of the memory cells MC includes a transistor WTr, a transistor RTr,and a capacitor CS. The transistor RTr in FIG. 32A has a backgate;application of a potential to the backgate can change the thresholdvoltage of the transistor RTr. The wiring BGL in FIG. 32A iselectrically connected to the backgates of the transistors RTr in thememory cells MC[1] to MC[n]. Instead of including one wiring BGLelectrically connected to the backgates of the transistor RTr in thememory cells MC[1] to MC[n], the semiconductor device in FIG. 32A mayinclude wirings BGL that are electrically connected to the respectivebackgates independently to supply different potentials to the backgates.

For example, a channel formation region of the transistor WTr preferablycontains a metal oxide described in Embodiment 4. Specifically, a metaloxide that contains at least one of indium, an element M (e.g.,aluminum, gallium, yttrium, or tin), and zinc functions as a wide gapsemiconductor; thus, a transistor containing the metal oxide in itschannel formation region has ultralow off-state current characteristics.When a transistor with such characteristics is used as the transistorWTr for retaining data, the memory cell MC can retain data for a longtime. As a result, the number of refreshing retained data can bereduced, leading to lower power consumption of the semiconductor device.

For a channel formation region of the transistor RTr, a materialachieving high field-effect mobility of the transistor is preferablyused. Using such a transistor allows the semiconductor device to operatefaster. Examples of the material contained in the channel formationregion of the transistor RTr include semiconductor materials such assilicon and the metal oxide described in Embodiment 4.

The transistor WTr functions as a write transistor, and the transistorRTr functions as a read transistor. The on/off state of the transistorWTr is switched by a potential supplied to the wiring WWL. The potentialof one electrode of the capacitor CS is controlled with the wiring RWL.The other electrode of the capacitor CS is electrically connected to agate of the transistor RTr. The other electrode of the capacitor CS canbe referred to as a memory node. In each of the memory cells MC, thememory node is electrically connected to a first terminal of thetransistor WTr.

A second terminal of the transistor WTr is electrically connected inseries with the first terminal of the transistor WTr in the adjacentmemory cell MC. Similarly, a first terminal of the transistor RTr iselectrically connected in series with a second terminal of thetransistor RTr in the adjacent memory cell MC. The second terminal ofthe transistor WTr in the memory cell MC[n] is electrically connected tothe wiring WBL. The second terminal of the transistor RTr in the memorycell MC[n] is electrically connected to the wiring RBL. In thisembodiment, a connection point of the second terminal of the transistorRTr in the memory cell MC[n] and the wiring RBL is referred to as a nodeN1, and the first terminal of the transistor RTr in the memory cellMC[1] is referred to as a node N2. Note that a selection transistor maybe connected in series with the transistor RTr in order to controlelectrical continuity between the node N1 and the wiring RBL. Similarly,a selection transistor may be connected in series with the transistorRTr in order to control electrical continuity between the node N2 and awiring connected to the node N2.

Note that one embodiment of the present invention is not limited to thesemiconductor device illustrated in FIG. 32A. One embodiment of thepresent invention can have a circuit configuration obtained byappropriately changing the circuit configuration of the semiconductordevice in FIG. 32A. For example, one embodiment of the present inventionmay be a semiconductor device in which the transistor WTr also has abackgate as illustrated in FIG. 32B. In the semiconductor device of FIG.32B including the components of the semiconductor device shown in FIG.32A, the transistors WTr in the memory cells MC[1] to MC[n] are providedwith backgates to which the wiring BGL is electrically connected. Asanother example, one embodiment of the present invention may be asemiconductor device in which the transistor RTr and the transistor WTrhave no backgate as illustrated in FIG. 32C.

To further increase the memory capacity of the semiconductor devices inFIGS. 32A to 32C, the semiconductor device shown in any of FIGS. 32A to32C is arranged in a matrix. For example, a circuit configurationillustrated in FIG. 33 is obtained when the semiconductor device in FIG.32B is arranged in a matrix.

In the semiconductor device illustrated in FIG. 33, the semiconductordevice in FIG. 32B is arranged in m columns (m is an integer of 1 ormore), and the wiring RWL and the wiring WWL are electrically connectedto and shared between the memory cells MC in the same row. That is, thesemiconductor device in FIG. 33 has a matrix of n rows and m columns andincludes the memory cells MC[1,1] to MC[n,m]. Accordingly, in thesemiconductor device in FIG. 33, electrical connection is establishedthrough the wirings RWL[1] to RWL[n], the wirings WWL[1] to WWL[n],wirings RBL[1] to RBL[m], wirings WBL[1] to WBL[m], and the wiringsBGL[1] to BGL[m]. Specifically, one electrode of the capacitor CS in thememory cell MC[0] is an integer of 1 to n, and i is an integer of 1 tom) is electrically connected to the wiring RWL[j]. The gate of thetransistor WTr in the memory cell MC[j,i] is electrically connected tothe wiring WWL[j]. The wiring WBL[i] is electrically connected to thesecond terminal of the transistor WTr in the memory cell MC[n,i]. Thewiring RBL[i] is electrically connected to the second terminal of thetransistor RTr in the memory cell MC[n,i].

FIG. 33 only illustrates the memory cell MC[1,1], the memory cellMC[1,i], the memory cell MC[1,m], the memory cell MC[j,1], the memorycell MC[j,i], the memory cell MC[j,m], the memory cell MC[n,1], thememory cell MC[n,i], the memory cell MC[n,m], the wiring RWL[1], thewiring RWL[j], the wiring RWL[n], the wiring WWL[1], the wiring WWL[j],the wiring WWL[n], the wiring RBL[1], the wiring RBL[i], the wiringRBL[m], the wiring WBL[1], the wiring WBL[i], the wiring WBL[m], thewiring BGL[1], the wiring BGL[i], the wiring BGL[m], the capacitor CS,the transistor WTr, the transistor RTr, the node N1, and the node N2 andomit the other wirings, elements, symbols, and reference numerals.

In FIG. 34, the semiconductor device in FIG. 32C is arranged in mcolumns (m is an integer of 1 or more). In the semiconductor device ofFIG. 34, the transistors in all the memory cells MC do not have abackgate; hence, the semiconductor device in FIG. 34 does not includethe wiring BGL. Note that the description of the semiconductor device inFIG. 33 is referred to for the semiconductor device in FIG. 34.

<Operation Method Example 2>

Next, an example of a method for operating the semiconductor device inany of FIGS. 32A to 32C will be described. Note that in the followingdescription, a low-level potential and a high-level potential do notrepresent any fixed potentials, and specific potentials may varydepending on wirings. For example, a low-level potential and ahigh-level potential supplied to the wiring WWL may be different from alow-level potential and a high-level potential supplied to the wiringRWL.

In this operation method example, the wiring BGL in FIGS. 32A and 32Bhas previously been supplied with a potential in a range where thetransistor RTr and/or the transistor WTr operate normally. Accordingly,the operations of the semiconductor devices in FIGS. 32A to 32C can beconsidered the same.

FIG. 35A is a timing chart showing an operation example for writing datainto the semiconductor device. FIG. 35B is a timing chart showing anoperation example for reading data from the semiconductor device. Thetiming charts in FIGS. 35A and 35B each show changes in potential levelof the wiring WWL[1], the wiring WWL[2], the wiring WWL[n], the wiringRWL[1], the wiring RWL[2], the wiring RWL[n], the node N1, and the nodeN2. As for the wiring WBL, data supplied to the wiring WBL is shown.

FIG. 35A shows an example of writing data D[1] to data D[n] into therespective memory cells MC[1] to MC[n]. Note that the data D[1] to thedata D[n] can be binary data, multilevel data, analog data, or the like.The data D[1] to the data D[n] are supplied from the wirings WBL. Thatis, in the circuit configuration of the semiconductor device in any ofFIGS. 32A to 32C, data is written into the memory cells MC sequentiallyfrom the memory cell MC[1] to the memory cell MC[n].

If data is to be written into the memory cell MC[1] after data iswritten into the memory cell MC[2], the data stored in the memory cellMC[2] is lost during data writing into the memory cell MC[1] unless thedata written into the memory cell MC[2] is read out in advance and savedin another place.

When data is written into the memory cell MC[i] (here, i is an integerof 2 to n) in the circuit configuration of the semiconductor device inany of FIGS. 32A to 32C, in order to prevent rewriting of data retainedin the memory cells MC[1] to MC[i−1], a low-level potential is suppliedto the wirings WWL[1] to WWL[i−1] so that the transistors WTr in thememory cells MC[1] to MC[i−1] are turned off. Thus, the data held ineach of the memory cells MC[1] to MC[i−1] can be protected.

Moreover, when data is written into the memory cell MC[i], since thedata is supplied from the wiring WBL, a high-level potential is suppliedto the wirings WWL[i] to WWL[n] so that the transistors WTr in thememory cells MC[i] to MC[n] are sufficiently turned on. Consequently,the data can be retained in the memory node of the memory cell MC[i].

When data is written into the semiconductor device having the circuitconfiguration in any of FIGS. 32A to 32C, the wiring RBL can becontrolled independently of the other wirings; therefore, the wiring RBLdoes not need to be set to a specific potential but can be set to alow-level potential, for example. That is, the potential of the node N1can be set to a low-level potential. The potential of the node N2 canalso be set to a low-level potential.

In light of the above, the operation example shown in the timing chartof FIG. 35A is described. At time T10, the wirings WWL[1] to WWL[n], thewirings RWL[1] to RWL[n], the wiring WBL, the node N1, and the node N2have a low-level potential.

At time T11, supply of a high-level potential to the wirings WWL[1] toWWL[n] starts. Thus, the transistors WTr in the memory cells MC[1] toMC[n] are sufficiently turned on between time T11 and time T12. The dataD[1] is supplied to the wiring WBL. Since the transistors WTr in thememory cells MC[1] to MC[n] are sufficiently turned on, the data D[1]reaches and is written into the memory node of the memory cell MC[1].

At time T12, supply of a low-level potential to the wiring WWL[1]starts, and the high-level potential is continuously supplied to thewirings WWL[2] to WWL[n]. Thus, between time T12 and time T13, thetransistor WTr in the memory cell MC[1] is turned off and thetransistors WTr in the memory cells MC[2] to MC[n] remain in asufficient on state. The data D[2] is supplied to the wiring WBL. Sincethe transistors WTr in the memory cells MC[2] to MC[n] are sufficientlyturned on, the data D[2] reaches and is written into the memory node ofthe memory cell MC[2]. The data D[1] stored in the memory cell MC[1] isnot lost by the write operation between time T12 and time T13 becausethe transistor WTr in the memory cell MC[1] is turned off.

Between time T13 and time T14, the data D[3] to the data D[n−1] aresequentially written into the memory cells MC[3] to MC[n−1] in the samemanner as the operation of writing the data D[1] into the memory cellMC[1] between time T11 and time T12 and the operation of writing thedata D[2] into the memory cell MC[2] between time T12 and time T13.Specifically, the transistors WTr in the memory cells MC[1] to MC[j−1]into which the data has been written (here, j is an integer of 3 to n−1)are turned off, the transistors WTr in the memory cells MC[j] to MC[n]into which the data has not been written yet are sufficiently turned on,and the data D[j] is supplied from the wiring WBL and written into thememory node of the memory cell MC[j]. Then, when writing of the dataD[j] into the memory cell MC[j] ends, the transistor WTr in the memorycell MC[j] is turned off, and the data D[j+1] is supplied from thewiring WBL and written into the memory node of the memory cell MC[j+1].Note that the write operation for j=n−1 refers to the followingoperation between time T14 and time T15.

At time T14, a low-level potential is supplied to the wirings WWL[1] toWWL[n−1] starts, and the high-level potential is continuously suppliedto the wiring WWL[n]. Thus, between time T14 and time T15, thetransistors WTr in the memory cells MC[1] to MC[n−1] are turned off andthe transistor WTr in the memory cell MC[n] remains in a sufficient onstate. The data D[n] is supplied to the wiring WBL. Since the transistorWTr in the memory cell MC[n] is sufficiently turned on, the data D[n]reaches and is written into the memory node of the memory cell MC[n].The data D[1] to the data D[n−1] stored in the respective memory cellsMC[1] to MC[n−1] are not lost by the write operation between time T14and time T15 because the transistors WTr in the memory cells MC[1] toMC[n−1] are turned off.

With the above operation, data can be written into the memory cells MCincluded in the semiconductor device shown in any of FIGS. 32A to 32C.

FIG. 35B shows an example of a timing chart for reading the data D[1] tothe data D[n] from the respective memory cells MC[1] to MC[n]. Here, thetransistors WTr need to be off to maintain the data stored in the memorycells MC. For that reason, the wirings WWL[1] to WWL[n] are set to alow-level potential during the operation of reading the data from thememory cells MC[1] to MC[n].

To read data in a specific memory cell MC in the semiconductor devicehaving the circuit configuration in any of FIGS. 32A to 32C, thetransistor RTr in the specific memory cell MC is made to operate in thesaturation region after the transistors RTr in the other memory cells MCare sufficiently turned on. That is, a current flowing between thesource and the drain of the transistor RTr in the specific memory cellMC is determined based on the source-drain voltage and data retained inthe specific memory cell MC.

For example, to read data retained in the memory cell MC[k] (here, k isan integer of 1 to n), a high-level potential is supplied to the wiringsRWL[1] to RWL[n] except the wiring RWL[k] so that the transistors RTr inthe memory cells MC[1] to MC[n] except the memory cell MC[k] aresufficiently turned on.

Meanwhile, in order to set the transistor RTr in the memory cell MC[k]to an on state corresponding to the retained data, the wiring RWL[k]needs to have the same potential as the wiring RWL[k] at the time ofwriting the data into the memory cell MC[k]. Here, the potential of thewiring RWL[k] in the write operation and the read operation isconsidered as a low-level potential.

For example, a potential of +3 V is supplied to the node N1, and apotential of 0 V is supplied to the node N2. Then, the node N2 is madefloating, and the potential of the node N2 is measured subsequently.When the wirings RWL[1] to RWL[n] except the wiring RWL[k] are set to ahigh-level potential, the transistors RTr in the memory cells MC[1] toMC[n] except the memory cell MC[k] are sufficiently turned on.Meanwhile, the voltage between the first terminal and the secondterminal of the transistor RTr in the memory cell MC[k] depends on thegate potential of the transistor RTr and the potential of the node N1;hence, the potential of the node N2 is determined based on the dataretained in the memory node of the memory cell MC[k].

In the above manner, the data stored in the memory cell MC[k] can beread out.

In light of the above, the operation example shown in the timing chartof FIG. 35B is described. At time T20, the wirings WWL[1] to WWL[n], thewirings RWL[1] to RWL[n], the wiring WBL, the node N1, and the node N2have a low-level potential. Specifically, the node N2 is floating. Thedata D[1] to the data D[n] are retained in the memory nodes of therespective memory cells MC[1] to MC[n].

Between time T21 and time T22, a low-level potential starts to besupplied to the wiring RWL[1], and a high-level potential starts to besupplied to the wirings RWL[2] to RWL[n]. Thus, the transistors RTr inthe memory cells MC[2] to MC[n] are sufficiently turned on between timeT21 and time T22. The transistor RTr in the memory cell MC[1] becomes anon state corresponding to the data D[1] retained in the memory node ofthe memory cell MC[1]. Moreover, a potential V_(R) is supplied to thewiring RBL. Consequently, the potential of the node N1 becomes V_(R),and the potential of the node N2 is determined based on the potentialV_(R) of the node N1 and the data retained in the memory node of thememory cell MC[1]. Here, the potential of the node N2 is denoted byV_(D[1]). By measurement of the potential V_(D[1]) of the node N2, thedata D[1] retained in the memory node of the memory cell MC[1] can beread out.

Between time T22 and time T23, a low-level potential starts to besupplied to the wirings RWL[1] to RWL[n]. A low-level potential issupplied to the node N2, and then the node N2 becomes floating. That is,the potentials of the wirings RWL[1] to RWL[n] and the node N2 betweentime T22 and time T23 become the same as those between time T20 and timeT21. Note that the wiring RBL may be continuously supplied with thepotential V_(R) or may be supplied with a low-level potential. In thisoperation example, the wiring RBL is continuously supplied with thepotential V_(R) after time T21.

Between time T23 and time T24, a low-level potential is supplied to thewiring RWL[2], and a high-level potential starts to be supplied to thewiring RWL[1] and the wirings RWL[3] to RWL[n]. Hence, the transistorsRTr in the memory cell MC[1] and the memory cells MC[3] to MC[n] aresufficiently turned on between time T23 and time T24. The transistor RTrin the memory cell MC[2] becomes an on state corresponding to the dataD[2] retained in the memory node of the memory cell MC[2]. The potentialV_(R) is continuously supplied to the wiring RBL. Consequently, thepotential of the node N2 is determined based on the potential V_(R) ofthe node N1 and the data retained in the memory node of the memory cellMC[2]. Here, the potential of the node N2 is denoted by V_(D[2]). Bymeasurement of the potential V_(D[2]) of the node N2, the data D[2]retained in the memory node of the memory cell MC[2] can be read out.

Between time T24 and time T25, the data D[3] to the data D[n−1] aresequentially read from the memory cells MC[3] to MC[n−1] in the samemanner as the operation of reading the data D[1] from the memory cellMC[1] between time T20 and time T22 and the operation of reading thedata D[2] from the memory cell MC[2] between time T22 and time T24.Specifically, to read the data D[j] from the memory cell MC[j] (here, jis an integer of 3 to n−1), the node N2 is set to a low-level potentialand is made floating, and then a high-level potential is supplied to thewirings RWL[1] to RWL[n] except the wiring RWL[j] so that thetransistors RTr in the memory cells MC[1] to MC[n] except the memorycell MC[j] are sufficiently turned on and the transistor RTr in thememory cell MC[j] is set to an on state corresponding to the data D[j].Next, the potential of the node N1 is set to V_(R), whereby thepotential of the node N2 becomes a potential corresponding to the dataD[j]; by measurement of this potential, the data D[j] can be read out.After the data D[j] stored in the memory cell MC[j] is read out, aspreparation for the next read operation, a low-level potential starts tobe supplied to the wirings RWL[1] to RWL[n] to set the node N2 to alow-level potential, and then the node N2 is made floating. Note thatthis preparation for j=n−1 refers to the operation between time T25 andtime T26.

Between time T25 and time T26, a low-level potential starts to besupplied to the wirings RWL[1] to RWL[n]. A low-level potential startsto be supplied to the node N2; the node N2 becomes floating after thepotential of the node N2 becomes the low-level potential. That is, thepotentials of the wirings RWL[1] to RWL[n] and the node N2 between timeT25 and time T26 become the same as those between time T20 and time T21.Note that the wiring RBL may be continuously supplied with the potentialV_(R) or may be supplied with a low-level potential. In this operationexample, the potential V_(R) starts to be supplied to the wiring RBL attime T21 and is continuously supplied to the wiring RBL at and aftertime T22.

At time T26, a low-level potential is supplied to the wiring RWL[n], anda high-level potential is supplied to the wirings RWL[1] to RWL[n−1].Thus, the transistors RTr in the memory cells MC[1] to MC[n−1] aresufficiently turned on between time T26 and time T27. The transistor RTrin the memory cell MC[n] becomes an on state corresponding to the dataD[n] retained in the memory node of the memory cell MC[n]. The potentialV_(R) is continuously supplied to the wiring RBL. Accordingly, thepotential of the node N2 is determined based on the potential V_(R) ofthe node N1 and the data retained in the memory node of the memory cellMC[n]. Here, the potential of the node N2 is denoted by V_(D[n]). Bymeasurement of the potential V_(D[n]) of the node N2, the data D[n] heldin the memory node of the memory cell MC[n] can be read out.

With the above operation, data can be read from each of the memory cellsMC in the semiconductor device shown in any of FIGS. 32A to 32C.

<Structure Example and Manufacturing Method Example 2>

For easy understanding of the structure of the semiconductor devicehaving the circuit configuration in any of FIGS. 32A to 32C, FIG. 33,and FIG. 34 described above, a method for manufacturing thesemiconductor device will be described below.

FIGS. 36A to 36C show a schematic example of the semiconductor deviceshown in FIG. 33 or FIG. 34. FIG. 36A is a perspective view of thesemiconductor device. FIG. 36B is a top view of FIG. 36A. FIG. 36C is across-sectional view along the dashed-dotted line A1-A2 in FIG. 36B.

The semiconductor device includes a structure body in which the wiringsRWL, the wirings WWL, and insulators (regions without a hatching patternin FIGS. 36A to 36C) are stacked.

An opening is formed in the structure body to penetrate the insulators,the wirings RWL, and the wirings WWL altogether. To provide the memorycell MC in the region AR that penetrates the wirings RWL and the wiringsWWL, an insulator, a conductor, and a semiconductor are formed in theopening. The conductor functions as the source electrode or the drainelectrode of the transistor WTr and/or the transistor RTr in the memorycell MC. The semiconductor functions as a channel formation region ofthe transistor WTr and/or the transistor RTr. Alternatively, withoutformation of the conductor, a channel formation region and alow-resistance region may be formed in the semiconductor and thelow-resistance region may serve as the source electrode or the drainelectrode of the transistor WTr and/or the transistor RTr. The regionwhere the insulator, the conductor, and the semiconductor are formed inthe opening is shown as the region HL in FIGS. 36A to 36C. In FIG. 36A,the region HL included inside the structure body is indicated by adashed line. Note that when the transistor included in the memory cellMC has a backgate, the conductor included in the region HL may functionas the wiring BGL electrically connected to the backgate.

In other words, FIGS. 36A to 36C illustrate that the semiconductordevice shown in any of FIGS. 32A to 32C is formed in the region SD1, andthe semiconductor device shown in FIG. 33 or FIG. 34 is formed in theregion SD2.

The region TM where the wiring RWL and the wiring WWL are exposedfunctions as a connection terminal for supplying a potential to thewiring RWL and the wiring WWL. That is, connecting wirings to the regionTM enables a potential to be supplied to the gates of the transistor WTrand the transistor RTr.

Note that the shape of the region TM is not limited to that in thestructure example shown in FIGS. 36A to 36C. The semiconductor device ofone embodiment of the present invention may be configured, for example,such that an insulator is formed over the region TM in FIGS. 36A to 36C,an opening is provided in the insulator, and the conductor PG is formedto fill the opening (FIGS. 37A to 37C). The wiring ER is formed over theconductor PG, whereby the wiring ER is electrically connected to thewiring RWL or the wiring WWL. In FIG. 37A, the conductor PG includedinside the structure body is indicated by a dashed line, and the dashedline representing the region HL is omitted.

In the following Manufacturing method example 2, a method for formingthe memory cell MC illustrated in any of FIGS. 32A to 34 in the regionAR will be described.

<<Manufacturing Method Example 2>>

FIGS. 38A to 42B and FIG. 43 are cross-sectional views for illustratingan example of manufacturing the semiconductor device in FIG. 32A, andare specifically cross-sectional views of the transistor WTr and thetransistor RTr in the channel length direction. In the cross-sectionalviews of FIGS. 38A to 43, some components are not illustrated forsimplification.

As illustrated in FIG. 38A, the semiconductor device in FIG. 32Aincludes an insulator 201A over a substrate (not shown), a conductor 231over the insulator 201A, an insulator 201B over the conductor 231, aconductor 232 over the insulator 201B, and an insulator 201C over theconductor 232. Note that a stack including these conductors andinsulators (sometimes also including an insulator, a conductor, and thelike other than the above depending on subsequent steps) is hereinafterreferred to as a stack 200.

For the substrate, any of the substrates described in Manufacturingmethod example 1 can be used, for example.

The conductor 231 functions as the wiring WWL in FIG. 32A, and theconductor 232 functions as the wiring RWL in FIG. 32A.

For the conductor 231 and the conductor 232, any of the materials usablefor the conductors 132A and 132B shown in Manufacturing method example 1can be used, for example. Moreover, each of the conductors 231 and 232may have a layered structure using a combination of at least two ofthese materials. The conductor 231 and the conductor 232 can be formedby any of the methods for forming the conductors 132A and 132B inManufacturing method example 1.

For the insulators 201A to 201C, any of the materials usable for theinsulators 101A to 101C shown in Manufacturing method example 1 can beused, for example. Moreover, each of the insulators 201A to 201C mayhave a layered structure using a combination of at least two of thesematerials. The insulators 201A to 201C can be formed by any of themethods for forming the insulators 101A to 101C in Manufacturing methodexample 1.

In the next step, as illustrated in FIG. 38B, an opening 291 is formedin the stack 200 shown in FIG. 38A through resist mask formation andetching treatment, for example.

The description in Manufacturing method example 1 is referred to for theresist mask formation and the etching treatment performed in themanufacturing step in FIG. 38B. Similarly, the description inManufacturing method example 1 is also referred to for resist maskformation and etching treatment to be performed later.

Then, as illustrated in FIG. 39A, the conductor 231 positioned on a sidesurface of the opening 291 is partly removed by etching treatment or thelike, and a recess portion 292 is formed on the side surface. Here, amaterial for the conductor 231 is selected such that the conductor 231is selectively removed in the stack 200 (e.g., a material with a higheretching rate than the insulators 201A to 201C and the conductor 232 isused).

In the subsequent step, as illustrated in FIG. 39B, an insulator 202 isdeposited in the recess portion 292 and on the side surface of theopening 291 shown in FIG. 39A.

The insulator 202 functions as a gate insulating film of the transistorWTr and an insulating film that is sandwiched between a pair ofelectrodes of the capacitor CS.

For the insulator 202, silicon oxide or silicon oxynitride can be used,for example. Alternatively, for the insulator 202, aluminum oxide,hafnium oxide, or an oxide containing aluminum and hafnium can be used,for example. The insulator 202 may be a stack including any of theabove.

To form the insulator 202, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method (e.g.,an LPCVD method or a PCVD method) may alternatively be used, forexample. As another deposition method, a sputtering method can sometimesbe used, for instance.

In the next step, as illustrated in FIG. 40A, a semiconductor 251 isdeposited in the recess portion and on the side surface of the opening291 shown in FIG. 39B. That is, the semiconductor 251 is formed incontact with the insulator 202.

For the semiconductor 251, a material containing a metal oxide describedin Embodiment 4 can be used, for example. Alternatively, for thesemiconductor 251, a material containing silicon can be used, forinstance.

The description of the method for forming the semiconductor 151 inManufacturing method example 1 is referred to for a method for formingthe semiconductor 251.

In the subsequent step, as illustrated in FIG. 40B, an insulator 203 isdeposited in the recess portion and on the side surface of the opening291 shown in FIG. 40A. That is, the insulator 203 is formed in contactwith the semiconductor 251.

Preferably, a component contained in the insulator 203 is not acomponent that would form a compound with a component contained in thepreviously formed semiconductor 251 at or around the interface betweenthe insulator 203 and the semiconductor 251. If the compound is formed,the compound is preferably an insulator or a compound that does notserve as a carrier in the semiconductor 251.

Silicon oxide can be used for the insulator 203, for example.

The description on the method for forming the insulator 202 is referredto for a method for forming the insulator 203.

In the subsequent step, as illustrated in FIG. 41A, part of theinsulator 203 positioned in the opening 291 is removed by resist maskformation and etching treatment or the like so that only the insulator203 in the recess portion remains. Thus, an insulator 203 a is formed.Note that at this time, part of the semiconductor 251 may be removed aslong as the insulator 202 is not exposed at the opening 291.

When a material containing a metal oxide is used for the semiconductor251, treatment for supplying impurities such as hydrogen may beperformed on the side surface of the opening 291. In that case, supplytreatment 20 illustrated in FIG. 41B is considered as a step (treatment)for supplying impurities such as hydrogen. The supply treatment 20 inFIG. 41B is performed on the insulator 203 a and a region 251 b of thesemiconductor 251. Note that the description for the supply treatment 11in FIG. 13 is referred to for the treatment for supplying impuritiessuch as hydrogen. In FIG. 41B, a compound 261A (a compound 261B) isshown as a compound that contains the component of the semiconductor 251and the impurities supplied by the supply treatment 20. By this step,the resistance of the region 251 b of the semiconductor 251 can belowered. Note that the supply treatment 20 described here is notnecessarily performed in some cases.

Meanwhile, when a material containing silicon is used for thesemiconductor 251, treatment for supplying an impurity may be performedon the side surface of the opening 291. In that case, the supplytreatment 20 illustrated in FIG. 41B is considered as a step (treatment)for supplying an impurity. FIG. 41B illustrates a step of performing theimpurity supply treatment 20 on the region 251 b of the semiconductor251 and the insulator 203 a. Note that heat treatment is preferablyperformed on the semiconductor device during the supply treatment 20. Asthe impurity, an n-type impurity (donor) such as phosphorus or arseniccan be used, for example. As another example, as the impurity, a p-typeimpurity (acceptor) such as boron, aluminum, or gallium can be used.Performing this step enables an impurity region 262A (an impurity region262B) to be formed on or around a surface of the region 251 b of thesemiconductor 251, thereby lowering the resistance of the region 251 bof the semiconductor 251. Note that the supply treatment 20 describedhere is not always necessary.

When a material containing one of a metal oxide and silicon is used forthe semiconductor 251, impurities are not supplied to a region 251 a ofthe semiconductor 251 because the insulator 203 a functions as a maskfor blocking impurities in the region 251 a where the insulator 203 a isformed in contact with the semiconductor 251.

In the subsequent step, as illustrated in FIG. 42A, an insulator 204 isdeposited on the side surface of the opening 291 shown in FIG. 41B.

For the insulator 204, an insulating material having a function ofinhibiting the passage of impurities such as water and hydrogen and thelike is preferably used, and aluminum oxide can be used, for example.Note that a material usable for the insulator 204 is not limited to theabove. For example, for the insulator 204, any of the materials usablefor the insulators 101A to 101C shown in Manufacturing method example 1can be used to form a film with a low concentration of impurities suchas water and hydrogen.

The description on the method for forming the insulator 202 is referredto for a method for forming the insulator 204.

In the next step, as illustrated in FIG. 42B, a semiconductor 252 isdeposited on the side surface of the opening 291 shown in FIG. 42A. Thatis, the semiconductor 252 is formed in contact with the insulator 204.

For the semiconductor 252, a material containing silicon can be used,for example. Alternatively, for the semiconductor 252, a semiconductormaterial such as a metal oxide described in Embodiment 4 can be used.

The description on the method for forming the semiconductor 251 isreferred to for a method for forming the semiconductor 252.

In the next step, as illustrated in FIG. 43, an insulator 205 isdeposited in contact with the semiconductor 252, and a conductor 233 isdeposited to fill the remaining opening 291.

For the insulator 205, any of the materials usable for the insulator 202can be used, for example. The insulator 205 may have a layered structureincluding a plurality of insulators.

The description on the method for forming the insulator 202 is referredto for a method for forming the insulator 205.

For the conductor 233, any of the materials usable for the conductors231 and 232 can be used, for example. The conductor 233 may have alayered structure including a plurality of conductors.

To form the conductor 233, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method mayalternatively be used, for example. As another deposition method, asputtering method, a sol-gel method, an electrophoretic method, or aspray method can sometimes be used, for instance.

In a region 281 illustrated in FIG. 43, the transistor WTr in FIG. 32Ais formed. Specifically, in the region 281, the conductor 231 functionsas the gate electrode of the transistor WTr, the semiconductors 251 inthe two regions 251 b function as the source electrode and the drainelectrode of the transistor WTr, and the semiconductor 251 in the region251 a functions as the channel formation region of the transistor WTr.When a material containing a metal oxide is used for the semiconductor251, the transistor WTr is an OS transistor.

In a region 282 illustrated in FIG. 43, the capacitor CS in FIG. 32A isformed. Specifically, in the region 282, the conductor 232 functions asone electrode of the capacitor CS, and the semiconductor 251 included inpart of the region 251 b functions as the other electrode of thecapacitor CS.

In a region 283 illustrated in FIG. 43, the transistor RTr in FIG. 32Ais formed. Specifically, in the region 283, part of the semiconductor251 in the region 251 b functions as the gate electrode of thetransistor RTr, the semiconductor 252 functions as the channel formationregion of the transistor RTr, and the conductor 233 functions as thebackgate electrode of the transistor RTr. When a material containing ametal oxide is used for the semiconductor 252, the transistor RTr is anOS transistor.

Through the steps from FIG. 38A to FIG. 43, the semiconductor deviceillustrated in FIG. 32A can be manufactured.

FIGS. 44A, 44B, and 44C are top views of the semiconductor device alongthe along the dashed-dotted lines C1-C2, C3-C4, and C5-C6 in FIG. 43.

One embodiment of the present invention is not limited to the structureexample of the semiconductor device illustrated in FIG. 43. In oneembodiment of the present invention, the structure of the semiconductordevice in FIG. 43 can be changed as appropriate.

For example, as described above, one embodiment of the present inventioncan be a semiconductor device in which the transistor WTr and thetransistor RTr are not provided with a backgate as illustrated in FIG.32C. To manufacture the semiconductor device shown in FIG. 32C, afterthe step in FIG. 42B in the process of manufacturing the semiconductordevice in FIG. 32A, the insulator 205 is deposited to fill the opening291 (see FIG. 45A).

Alternatively, the insulator 205 may have a layered structure. Aplurality of insulator materials can be used in combination, forexample, as illustrated in FIG. 45B in which silicon oxide is used foran insulator 205A in contact with the semiconductor 252 and aluminumoxide, hafnium oxide, or the like is used for an insulator 205B incontact with the insulator 205A.

The description on the method for forming the insulator 202 is referredto for a method for forming each of the insulators 205A and 205B.

FIGS. 46A, 46B, and 46C are top views of the semiconductor device alongthe along the dashed-dotted lines C1-C2, C3-C4, and C5-C6 in FIG. 45A.Unlike the semiconductor device in FIG. 43, the semiconductor device inFIG. 45A has a structure without the conductor 233; hence, the top viewsin FIGS. 46A to 46C are different from those in FIGS. 44A to 44C in thatthe conductor 233 is not provided inside the insulator 205.

For example, part of the process for manufacturing the semiconductordevice of one embodiment of the present invention may be changed. FIGS.47A and 47B illustrate steps for forming a low-resistance region in theregion 251 b of the semiconductor 251 in a manner different from that inFIG. 41B.

FIG. 47A shows a step for forming a conductor 239 on the side surface ofthe opening 291 after the step in FIG. 41A. Specifically, the conductor239 is formed in contact with the insulator 203 a and the region 251 bof the semiconductor 251. At this time, with the conductor 239 incontact with the semiconductor 251, the compound 261A (the compound261B) or the impurity region 262A (the impurity region 262B) is formedin the region 251 b of the semiconductor 251, as in the steps shown inFIGS. 19A and 19B. That is, the resistance of the region 251 b of thesemiconductor 251 is lowered. Note that the description for FIGS. 19Aand 19B is referred to for the resistance reduction.

A material for the conductor 239 can be selected from the materialsusable for the conductor 139 described using FIGS. 19A and 19B, on thebasis of the material contained in the semiconductor 251.

By the above manufacturing method, the region 251 b of the semiconductor251 can be formed as a low-resistance region and the region 251 a of thesemiconductor 251 can be formed as a channel formation region. Note thatthe region 251 b serving as the low-resistance region corresponds to thefirst terminal and/or the second terminal the transistor WTr (the gateof the transistor RTr); hence, the electric resistance between thetransistors WTr, which are electrically connected in series, can belowered by the above manufacturing method.

To form the conductor 239, a deposition method achieving high stepcoverage is preferably employed. As the deposition method achieving highstep coverage, an ALD method is preferably used, and a CVD method mayalternatively be used, for example. As another deposition method, asputtering method, a sol-gel method, an electrophoretic method, or aspray method can sometimes be used, for instance.

In the next step, as illustrated in FIG. 47B, the conductor 239 on theside surface of the opening 291 is removed using etching treatment orthe like. At this time, the interface between the conductor 239 and theinsulator 203 a, which overlaps the region 251 a, and a region aroundthe interface may be partly removed as well.

Subsequently, the steps from FIG. 42A to FIG. 43 are performed, wherebythe semiconductor device in which the low-resistance region is formed inthe region 251 b of the semiconductor 251 can be manufactured throughthe manufacturing steps different from that shown in FIG. 41B.

Another method for forming the low-resistance region that is differentfrom that shown in FIGS. 47A and 47B will be described. FIG. 48Aillustrates a step for forming an insulator 207 on the side surface ofthe opening 291 after the step in FIG. 41A.

When the semiconductor 251 is a material containing a metal oxide, theinsulator 207 preferably contains silicon nitride, for example. When thesemiconductor 251 is in contact with the insulator 207, nitrogen,nitride, and other components included in the insulator 207 may diffuseinto the semiconductor 251. At this time, heat treatment may or may notbe performed on the stack 200. When nitrogen, nitride, and othercomponents in the insulator 207 diffuse into the semiconductor 251, inFIG. 48A, the compound 261A (the compound 261B) may be formed in thesemiconductor 251 at and around the interface with the insulator 207 bynitrogen, nitride, and other components diffused from the insulator 207.In that case, the resistance of the region 251 b of the semiconductor251 is lowered. In other words, the resistance of the source electrodeor the drain electrode of the transistor WTr can sometimes be lowered.

When the semiconductor 251 is a material containing silicon, theinsulator 207 preferably contains an impurity (an element or an ion) tobe diffused into the semiconductor 251, for example. When an n-typeimpurity (donor) is used as the impurity, phosphorus or arsenic can beused, for example. When a p-type impurity (acceptor) is used as theimpurity, boron, aluminum, or gallium can be used, for example.

When the semiconductor 251 is in contact with the insulator 207, animpurity (an element or an ion) contained in the insulator 207 maydiffuse into the semiconductor 251. At this time, heat treatment may ormay not be performed on the stack 200. That is, the impurity region maybe formed in the semiconductor 251 at or around the interface with theinsulator 207. Consequently, carriers are generated in the region 251 bof the semiconductor 251 or in the semiconductor 251 around theinterface with the insulator 207, resulting in lower resistance of theregion 251 b in some cases.

The description on the method for forming the insulator 202 is referredto for a method for forming the insulator 207.

In the next step, an insulator 208 is deposited on the side surface ofthe opening 291, and then the same steps as in FIG. 42B and FIG. 43 areperformed, whereby a semiconductor device illustrated in FIG. 48B can befabricated.

When the semiconductor 252 contains a metal oxide, the insulator 208 canbe, for example, an insulating material for preventing nitrogen,nitride, and other components of the insulator 207 from diffusing intothe semiconductor 252. In this case, silicon oxide or aluminum oxide canbe used for the insulator 208, for instance. Note that when thesemiconductor 252 contains silicon, the insulator 208 may or may not beformed.

The description on the method for forming the insulator 202 is referredto for a method for forming the insulator 208.

FIGS. 49A, 49B, and 49C are top views of the semiconductor device alongthe along the dashed-dotted lines C1-C2, C3-C4, and C5-C6 in FIG. 48B.The semiconductor device in FIG. 48B includes the insulator 207 and theinsulator 208 between the semiconductor 251 and the semiconductor 252;accordingly, in the top views of FIGS. 49A to 49C, the insulator 204 inFIGS. 44A to 44C is replaced with the stack of the insulator 207 and theinsulator 208.

As another example, when the semiconductor 251 is a material containinga metal oxide in one embodiment of the present invention, thesemiconductor 251 can have a three-layer structure as in a semiconductordevice illustrated in FIG. 50. In the semiconductor device in FIG. 50,the three-layer structure of the semiconductor 251 can be constitutedsuch that a semiconductor 253A, a semiconductor 253B, and asemiconductor 253C are sequentially formed as the semiconductor 251 bythe step shown in FIG. 40A in the process of manufacturing thesemiconductor device in FIG. 32A.

FIGS. 51A, 51B, and 51C are top views of the semiconductor device alongthe along the dashed-dotted lines C1-C2, C3-C4, and C5-C6 in FIG. 50. Asan example, the semiconductor device in FIG. 50 employs a three-layerstructure where the semiconductors 253A, 253B, and 253C are sequentiallydeposited in this order on the insulator 202; hence, in the top views ofFIGS. 51A to 51C, the semiconductor 251 in FIGS. 44A to 44C has athree-layer structure.

Note that the description of the semiconductors 152A, 152B, and 152C inManufacturing method example 1 is referred to for the semiconductors253A, 253B, and 253C. Moreover, the description for FIG. 22 inManufacturing method example 1 is referred to for the effects of thestructure in FIG. 50.

As another example, in one embodiment of the present invention, thestructure of the gate electrode of the transistor WTr may be changedfrom that in FIG. 43 in order to improve the reliability of thetransistor WTr. FIGS. 52A and 52B and FIGS. 53A and 53B illustrate anexample of a method for manufacturing such a semiconductor device.

In a step illustrated in FIG. 52A, the conductor 231 positioned on theside surface of the opening 291 is partly removed by etching treatmentor the like in FIG. 39B, and a recess portion 294 is formed on the sidesurface. Note that the recess portion 294 may be formed deeper than therecess portion 292 shown in FIG. 39A.

In the subsequent step in FIG. 52B, a semiconductor 254 is deposited onthe side surface of the opening 291 and in the recess portion 294 inFIG. 52A.

For the semiconductor 254, any of the materials usable for thesemiconductor 153 in Manufacturing method example 1 can be used, forexample.

The description on the method for forming the semiconductor 251 isreferred to for a method for forming the semiconductor 254.

In the next step, as illustrated in FIG. 53A, part of the remainingsemiconductor 254 in the recess portion 294 and the semiconductor 254positioned on the side surface of the opening 291 are removed by resistmask formation and etching treatment or the like so that thesemiconductor 254 remains in part of the recess portion 294. Thus, asemiconductor 254 a is formed.

Subsequently, steps similar to those in FIGS. 39B to 43 are performed,thereby constituting a semiconductor device illustrated in FIG. 53B.Note that the description for FIGS. 27A to 28B in Manufacturing methodexample 1 is referred to for the effects of the structure in FIG. 53B.

FIGS. 54A, 54B, and 54C are top views of the semiconductor device alongthe along the dashed-dotted lines C1-C2, C3-C4, and C5-C6 in FIG. 53B.In the semiconductor device in FIG. 53B, the semiconductor 254 a isincluded between the conductor 231 and the insulator 202 in the region251 a, which is different from the semiconductor device in FIG. 43.Accordingly, the top view in FIG. 54C shows a structure where thesemiconductor 254 a is included between the conductor 231 and theinsulator 202. Note that the top views in FIGS. 54A and 54B along thedashed-dotted lines C1-C2 and C3-C4 are approximately the same as thosein FIGS. 44A and 44B in some cases.

According to Manufacturing method example 1 or 2 described above, asemiconductor device capable of retaining a large amount of data can bemanufactured.

Here, FIG. 55 illustrates a structure example in which the semiconductordevice with the cross-sectional structure in FIG. 14B (with the circuitconfiguration in FIG. 1A) is arranged to form the cell array shown inFIG. 2. Similarly, FIG. 56 illustrates a structure example in which thesemiconductor device with the cross-sectional structure in FIG. 43 (withthe circuit configuration in FIG. 32A) is arranged to form the cellarray. Note that the region SD1 corresponds to the memory cells MC. Asillustrated in FIG. 55, an opening is provided to penetrate a structurebody in which the conductors serving as the wirings WL and theinsulators are stacked, and the semiconductor device is manufacturedaccording to Manufacturing method example 1 described above, whereby thecircuit configuration in FIG. 1A can be obtained. Furthermore, asillustrated in FIG. 56, an opening is provided to penetrate a structurebody in which the conductors serving as the wirings RWL or the wiringsWWL and the insulators are stacked, and the semiconductor device ismanufactured according to Manufacturing method example 2 describedabove, whereby the circuit configuration in FIG. 32A can be obtained.

<Connection Examples with Peripheral Circuit>

A peripheral circuit for the memory cell array, such as a read circuitor a precharge circuit, may be provided below the semiconductor deviceshown in Manufacturing method example 1 or 2. In this case, Sitransistors are formed on a silicon substrate or the like to configurethe peripheral circuit, and then the semiconductor device of oneembodiment of the present invention is formed over the peripheralcircuit according to Manufacturing method example 1 or 2. FIG. 57A is across-sectional view in which the peripheral circuit is formed usingplanar Si transistors and the semiconductor device of one embodiment ofthe present invention is formed over the peripheral circuit. FIG. 58A isa cross-sectional view in which the peripheral circuit is formed usingFIN-type Si transistors and the semiconductor device of one embodimentof the present invention is formed over the peripheral circuit. As anexample, the semiconductor device illustrated in each of FIGS. 57A and58A has the structure in FIG. 14B.

In FIG. 57A and FIG. 58A, the Si transistors configuring the peripheralcircuit are formed on a substrate 1700. An element separation layer 1701is provided between a plurality of Si transistors. Conductors 1712 areformed as a source and a drain of the Si transistor. Although not shown,a conductor 1730 extends in the channel width direction to be connectedto another Si transistor or the conductor 1712.

As the substrate 1700, a single crystal semiconductor substrate or apolycrystalline semiconductor substrate of silicon or silicon carbide, acompound semiconductor substrate of silicon germanium, an SOI substrate,or the like can be used.

Alternatively, a glass substrate, a quartz substrate, a plasticsubstrate, a metal substrate, a flexible substrate, an attachment film,paper including a fibrous material, or a base film, for example, may beused as the substrate 1700. A semiconductor element may be formed usingone substrate and then transferred to another substrate. As an example,a single crystal silicon wafer is used as the substrate 1700 in FIG. 57Aand FIG. 58A.

Here, the details of the Si transistors are described. FIG. 57A shows across section of the planar Si transistor in the channel lengthdirection, and FIG. 57B shows its cross section in the channel widthdirection. The Si transistor includes a channel formation region 1793 ina well 1792, low-concentration impurity regions 1794 andhigh-concentration impurity regions 1795 (also collectively referred tosimply as impurity regions), conductive regions 1796 in contact with theimpurity regions, a gate insulating film 1797 over the channel formationregion 1793, a gate electrode 1790 over the gate insulating film 1797,and sidewall insulating layers 1798 and 1799 on side surfaces of thegate electrode 1790. Note that the conductive region 1796 may be formedusing metal silicide or the like.

FIG. 58A shows a cross section of the FIN-type Si transistor in thechannel length direction, and FIG. 58B shows its cross section in thechannel width direction. In the Si transistor illustrated in FIGS. 58Aand 58B, the channel formation region 1793 has a projecting portion, andthe gate insulating film 1797 and the gate electrode 1790 are providedalong the side and top surfaces of the channel formation region 1793.Although the projecting portion is formed by processing of part of thesemiconductor substrate in this embodiment, a semiconductor layer with aprojecting portion may be formed by processing of an SOI substrate.

An insulator 301 is provided above the circuit formed using the Sitransistors, the conductor 1712, the conductor 1730, and the like overthe substrate 1700. A conductor 311A and a conductor 311B forelectrically connecting to the circuit are formed to so as be embeddedin the insulator 301. When the channel formation region of the celltransistor CTr contains a metal oxide, a material with barrierproperties against hydrogen and the like is preferably used for theinsulator 301 and the conductors 311A and 311B, in which case diffusionof hydrogen from the Si transistor into the cell transistor CTr throughat least one of the insulator 301, the conductor 311A, and the conductor311B is suppressed.

For the insulator 301, any of the materials usable for the insulators101A to 101C can be used.

For the conductors 311A and 311B, tantalum nitride, which has barrierproperties against hydrogen, is preferably used, for example. The use ofa stack including tantalum nitride and tungsten, which has highconductivity, can inhibit diffusion of hydrogen from the Si transistorwhile the conductors 311A and 311B maintain the conductivity as awiring.

Note that the reference numerals in FIGS. 58A and 58B are the same asthose in FIGS. 57A and 57B.

Note that the insulators, the conductors, the semiconductors, and thelike disclosed in this specification and the like can be formed by aphysical vapor deposition (PVD) method or a chemical vapor deposition(CVD) method. Examples of a PVD method include a sputtering method, aresistance heating evaporation method, an electron beam evaporationmethod, and a pulsed laser deposition (PLD) method. Examples of a CVDmethod include a plasma CVD method and a thermal CVD method. Examples ofa thermal CVD method include a metal organic chemical vapor deposition(MOCVD) method and an atomic layer deposition (ALD) method.

Since plasma is not used for deposition, a thermal CVD method has anadvantage that no defect due to plasma damage is generated.

Deposition by a thermal CVD method may be performed in such a mannerthat a source gas and an oxidizer are supplied to a chamber at a time,the pressure in the chamber is set to an atmospheric pressure or areduced pressure, and the source gas and the oxidizer react with eachother in the vicinity of a substrate or over the substrate.

Deposition by an ALD method may be performed in such a manner that thepressure in a chamber is set to an atmospheric pressure or a reducedpressure, source gases for reaction are sequentially introduced into thechamber, and then the sequence of the gas introduction is repeated. Forexample, two or more kinds of source gases are sequentially supplied tothe chamber by switching of corresponding switching valves (alsoreferred to as high-speed valves) such that the source gases are notmixed. For example, a first source gas is introduced, an inert gas(e.g., argon or nitrogen) or the like is introduced at the same time asor after the introduction of the first source gas, and then a secondsource gas is introduced. Note that in the case where the first sourcegas and the inert gas are introduced at a time, the inert gas serves asa carrier gas, and the inert gas may also be introduced at the same timeas the introduction of the second source gas. Alternatively, the secondsource gas may be introduced after the first source gas is exhausted byvacuum evacuation instead of the introduction of the inert gas. Thefirst source gas is adsorbed on a surface of a substrate to form a firstthin layer, and then the second source gas is introduced to react withthe first thin layer; thus, a second thin layer is stacked over thefirst thin layer, and a thin film is formed as a result. The sequence ofthe gas introduction is controlled and repeated a plurality of timesuntil a desired thickness is obtained, whereby a thin film withexcellent step coverage can be formed. The thickness of the thin filmcan be adjusted by the number of repetition times of the sequence of thegas introduction; therefore, an ALD method makes it possible to adjust athickness accurately and thus is suitable for manufacturing a minuteFET.

A variety of films such as the metal film, the semiconductor film, andthe inorganic insulating film described thus far can be formed by athermal CVD method such as a MOCVD method or an ALD method. For example,to form an In—Ga—Zn—O film, trimethylindium (In(CH₃)₃), trimethylgallium(Ga(CH₃)₃), and dimethylzinc (Zn(CH₃)₂) are used. Without limitation tothe above combination, triethylgallium (Ga(C₂H₅)₃) can be used insteadof trimethylgallium, and diethylzinc (Zn(C₂H₅)₂) can be used instead ofdimethylzinc.

For example, when a hafnium oxide film is formed by a depositionapparatus employing ALD, two kinds of gases, i.e., ozone (O₃) as anoxidizer and a source gas obtained by vaporization of liquid containinga solvent and a hafnium precursor compound (hafnium alkoxide or hafniumamide such as tetrakis(dimethylamide)hafnium (TDMAH, Hf[N(CH₃)₂]₄)) areused. Alternatively, tetrakis(ethylmethylamide)hafnium may be used, forinstance.

For example, when an aluminum oxide film is formed by a depositionapparatus employing ALD, two kinds of gases, i.e., H₂O as an oxidizerand a source gas obtained by vaporization of liquid containing a solventand an aluminum precursor compound (e.g., trimethylaluminum (TMA,Al(CH₃)₃)) are used. Alternatively, tris(dimethylamide)aluminum,triisobutylaluminum, aluminumtris(2,2,6,6-tetramethyl-3,5-heptanedionate), or the like may be used.

For example, when a silicon oxide film is formed by a depositionapparatus using ALD, hexachlorodisilane is adsorbed on a surface wherethe film is to be formed, and radicals of an oxidizing gas (e.g., O₂ ordinitrogen monoxide) are supplied to react with the adsorbate.

For example, when a tungsten film is formed by a deposition apparatususing ALD, a WF₆ gas and a B₂H₆ gas are sequentially introduced to forman initial tungsten film, and then a WF₆ gas and an H₂ gas aresequentially introduced to form a tungsten film. Note that a SiH₄ gasmay be used instead of a B₂H₆ gas.

For example, when an oxide semiconductor film, e.g., an In—Ga—Zn—O filmis formed by a deposition apparatus employing ALD, an In(CH₃)₃ gas andan O₃ gas) are sequentially introduced to form an In—O layer, a Ga(CH₃)₃gas and an O₃ gas) are sequentially introduced to form a GaO layer, andthen a Zn(CH₃)₂ gas and an O₃ gas) are sequentially introduced to form aZnO layer. Note that the order of these layers is not limited to thisexample. A mixed oxide layer such as an In—Ga—O layer, an In—Zn—O layer,or a Ga—Zn—O layer may be formed with the use of these gases. Note thatalthough an H₂O gas that is obtained by bubbling water with an inert gassuch as Ar may be used instead of an O₃ gas), it is preferable to use anO₃ gas), which does not contain H. Furthermore, an In(C₂H₅)₃ gas may beused instead of an In(CH₃)₃ gas. A Ga(C₂H₅)₃ gas may be used instead ofa Ga(CH₃)₃ gas. Moreover, a Zn(CH₃)₂ gas may be used.

Note that at least two of the structure examples of the semiconductordevices described in this embodiment can be combined as appropriate.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 2

In this embodiment, a memory device including the semiconductor devicedescribed in the foregoing embodiment will be described.

FIG. 59 illustrates a structure example of a memory device. A memorydevice 2600 includes a peripheral circuit 2601 and a memory cell array2610. The peripheral circuit 2601 includes a row decoder 2621, a wordline driver circuit 2622, a bit line driver circuit 2630, an outputcircuit 2640, and a control logic circuit 2660.

The semiconductor device illustrated in any of FIGS. 1A and 1B and FIGS.32A to 32C in Embodiment 1 can be used for the memory cell array 2610.

The bit line driver circuit 2630 includes a column decoder 2631, aprecharge circuit 2632, a sense amplifier 2633, and a write circuit2634. The precharge circuit 2632 has a function of precharging thewirings SL, BL, RBL, and the like, which are described in Embodiment 1but not shown in FIG. 59, to a predetermined potential. The senseamplifier 2633 has a function of obtaining a potential (or a current)read from the memory cell MC as a data signal and amplifying the datasignal. The amplified data signal is output as a digital data signalRDATA from the memory device 2600 through the output circuit 2640.

As power supply voltages, a low power supply voltage (VSS), a high powersupply voltage (VDD) for the peripheral circuit 2601, and a high powersupply voltage (VIL) for the memory cell array 2610 are supplied to thememory device 2600 from the outside.

Control signals (CE, WE, RE), an address signal ADDR, and a data signalWDATA are input to the memory device 2600 from the outside. The addresssignal ADDR is input to the row decoder 2621 and the column decoder2631. The data signal WDATA is input to the write circuit 2634.

The control logic circuit 2660 processes the signals (CE, WE, RE) inputfrom the outside, and generates control signals for the row decoder 2621and the column decoder 2631. The signal CE is a chip enable signal, thesignal WE is a write enable signal, and the signal RE is a read enablesignal. Signals processed by the control logic circuit 2660 are notlimited to those listed above, and other control signals may be input asnecessary.

Note that whether the circuits and signals described above are providedor not can be determined as appropriate when needed.

When a p-channel Si transistor and a transistor whose channel formationregion contains an oxide semiconductor described in Embodiment 4(preferably an oxide containing In, Ga, and Zn) are used in the memorydevice 2600, the memory device 2600 can be reduced in size. In addition,the memory device 2600 can be reduced in power consumption. Furthermore,the memory device 2600 can be increased in operating speed. Particularlywhen the Si transistors are only p-channel ones, the manufacturing costcan be reduced.

Note that the configuration of this embodiment is not limited to thatshown in FIG. 59. The configuration may be changed as appropriate; forexample, part of the peripheral circuit 2601 (e.g., the prechargecircuit 2632 and/or the sense amplifier 2633) may be provided below thememory cell array 2610.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 3

Referring to FIGS. 60A to 60E, this embodiment will show an examplewhere the semiconductor device described in the foregoing embodiment isused as a memory device in an electronic component.

FIG. 60A shows an example in which the semiconductor device of theforegoing embodiment is used as a memory device in an electroniccomponent. Note that an electronic component is also referred to as asemiconductor package or an IC package. For the electronic component,there are various standards and names corresponding to the direction orthe shape of terminals; hence, one example of the electronic componentwill be described in this embodiment.

A semiconductor device including transistors, such as one described inEmbodiment 1, is completed through the assembly process (post-process,or packaging and testing process) for integrating detachable componentson a printed circuit board.

The post-process can be completed through steps shown in FIG. 60A.Specifically, after an element substrate obtained in the precedingprocess (wafer process) is completed (Step STP1), a rear surface of thesubstrate is ground (Step STP2). The substrate is thinned in this stepto reduce warpage or the like of the substrate caused in the waferprocess and to reduce the size of the component itself.

After the rear surface of the substrate is ground, a dicing step isperformed to divide the substrate into a plurality of chips (Step STP3).Then, the divided chips are separately picked up to be mounted on andbonded to a lead frame in a die bonding process (Step STP4). To bond achip and a lead frame in the die bonding process, resin bonding,tape-automated bonding, or the like is selected as appropriate dependingon a product. Note that in the die bonding process, the chip may bemounted on and bonded to an interposer.

Note that in this embodiment, when an element is formed on one surfaceof a substrate, the other surface (a surface on which the element is notformed) is referred to as a rear surface.

Next, wiring bonding for electrically connecting a lead of the leadframe and an electrode on the chip through a metal fine line (wire) isperformed (Step STP5). A silver line or a gold line can be used as themetal wire. Ball bonding or wedge bonding can be used for the wirebonding.

The wire-bonded chip is subjected to a molding step of sealing the chipwith an epoxy resin or the like (Step STP6). By the molding step, theinside of the electronic component is filled with a resin, therebyreducing damage to the circuit portion and the wire embedded in theelectronic component caused by external mechanical force as well asreducing deterioration of characteristics due to moisture or dust.

Next, plate processing is performed on the lead of the lead frame. Then,the lead is cut and processed into a predetermined shape (Step STP7).This plate processing prevents rust of the lead and enables morereliable soldering at the time of mounting the electronic component on aprinted board in a later step.

Subsequently, printing (marking) is performed on a surface of thepackage (Step STP8). After a final testing step (Step STP9), theelectronic component is completed (Step STP10).

Since the above electronic component can include the semiconductordevice described in the foregoing embodiment, it is possible to obtain ahighly reliable electronic component.

FIG. 60B is a perspective schematic diagram of a completed electroniccomponent. FIG. 60B shows a perspective schematic diagram of a quad flatpackage (QFP) as an example of the electronic component. An electroniccomponent 4700 in FIG. 60B includes a lead 4701 and a circuit portion4703. The electronic component 4700 in FIG. 60B is mounted on a printedcircuit board 4702, for example. A plurality of electronic components4700 that are combined and electrically connected to each other over theprinted board 4702 can be equipped in an electronic device. A completedcircuit board 4704 is provided in an electronic device or the like.

Note that one embodiment of the present invention is not limited to theelectronic component 4700 and may be the element substrate fabricated inStep STP1. In addition, the element substrate of one embodiment of thepresent invention includes an element substrate that has been subjectedto Step STP2 where the rear surface of the substrate is ground.Furthermore, the element substrate of one embodiment of the presentinvention includes an element substrate that has been subjected to StepSTP3 where the dicing step is performed. For example, a semiconductorwafer 4800 illustrated in FIG. 60C corresponds to such an elementsubstrate. In the semiconductor wafer 4800, a plurality of circuitportions 4802 are formed on a top surface of a wafer 4801. A portionwithout the circuit portions 4802 on the top surface of the wafer 4801is a spacing 4803, and part of the spacing 4803 serves as a regionsubjected to dicing.

The dicing is carried out along scribe lines SCL1 and scribe lines SCL2(sometimes referred to as dicing lines or cutting lines) indicated bydashed-dotted lines. To perform the dicing step easily, the spacing 4803is preferably arranged such that a plurality of scribe lines SCL1 areparallel to each other, a plurality of scribe lines SCL2 are parallel toeach other, and the scribe lines SCL1 and the scribe lines SCL2intersect each other perpendicularly.

With the dicing step, a chip 4800 a shown in FIG. 60D can be cut outfrom the semiconductor wafer 4800. The chip 4800 a includes a wafer 4801a, the circuit portion 4802, and a spacing 4803 a. Note that it ispreferable to make the spacing 4803 a as small as possible. Here, it ispreferred that the width of the spacing 4803 between adjacent circuitportions 4802 be substantially the same as the length of margin forcutting the scribe line SCL1 or the scribe line SCL2.

The shape of the element substrate of one embodiment of the presentinvention is not limited to the shape of the semiconductor wafer 4800illustrated in FIG. 60C. For example, the element substrate may be arectangular semiconductor wafer 4810 shown in FIG. 60E. The shape of theelement substrate can be changed as appropriate, depending on a processfor fabricating an element and an apparatus for fabricating an element.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 4

In this embodiment, a metal oxide contained in a channel formationregion of an OS transistor used in the foregoing embodiment will bedescribed.

The metal oxide preferably contains at least indium or zinc, andparticularly preferably contains both indium and zinc. In addition, themetal oxide preferably contains aluminum, gallium, yttrium, tin, or thelike. Furthermore, the metal oxide may contain one or more elementsselected from boron, silicon, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, magnesium, and the like.

Here, the case where the metal oxide is an In-M-Zn oxide containingindium, an element M, and zinc is considered. The element M is aluminum,gallium, yttrium, tin, or the like. Other elements that can be used asthe element M include boron, silicon, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, and magnesium. Note that two or more of the above elements maybe used in combination as the element M.

Next, preferred ranges of the atomic ratio of indium, the element M, andzinc contained in the metal oxide according to the present inventionwill be described with reference to FIGS. 61A to 61C. Note that theproportion of oxygen atoms is not shown in FIGS. 61A to 61C. The termsof the atomic ratio of indium, the element M, and zinc contained in themetal oxide are denoted by [In], [M], and [Zn], respectively.

In FIGS. 61A to 61C, broken lines indicate a line where the atomic ratio[In]:[M]:[Zn] is (1+α):(1−α):1, where −1≤α≤1, a line where the atomicratio [In]:[M]:[Zn] is (1+α):(1−α):2, a line where the atomic ratio[In]:[M]:[Zn] is (1+α):(1−α):3, a line where the atomic ratio[In]:[M]:[Zn] is (1+α):(1−α):4, and a line where the atomic ratio[In]:[M]:[Zn] is (1+α):(1−α):5.

Dashed-dotted lines indicate a line where the atomic ratio [In]:[M]:[Zn]is 5:1:β, where β≥0, a line where the atomic ratio [In]:[M]:[Zn] is2:1:β, a line where the atomic ratio [In]:[M]:[Zn] is 1:1:β, a linewhere the atomic ratio [In]:[M]:[Zn] is 1:2:β, a line where the atomicratio [In]:[M]:[Zn] is 1:3:β, and a line where the atomic ratio[In]:[M]:[Zn] is 1:4:β.

A metal oxide having an atomic ratio [In]:[M]:[Zn] of 0:2:1 or around0:2:1 in FIGS. 61A to 61C tends to have a spinel crystal structure.

A plurality of phases (e.g., two phases or three phases) exist in themetal oxide in some cases. For example, with an atomic ratio[In]:[M]:[Zn] that is close to 0:2:1, two phases of a spinel crystalstructure and a layered crystal structure are likely to exist. Inaddition, with an atomic ratio [In]:[M]:[Zn] that is close to 1:0:0, twophases of a bixbyite crystal structure and a layered crystal structureare likely to exist. In the case where a plurality of phases exist inthe metal oxide, a grain boundary might be formed between differentcrystal structures.

A region A in FIG. 61A shows an example of the preferred ranges of theatomic ratio of indium to the element M and zinc contained in a metaloxide.

A metal oxide with a higher content of indium can have high carriermobility (electron mobility). Therefore, a metal oxide with a highindium content has higher carrier mobility than a metal oxide with a lowindium content.

In contrast, when the indium content and the zinc content in a metaloxide become lower, the carrier mobility becomes lower. Thus, with anatomic ratio [In]:[M]:[Zn] of 0:1:0 or around 0:1:0 (e.g., a region C inFIG. 61C), insulation performance becomes better.

Accordingly, a metal oxide of one embodiment of the present inventionpreferably has an atomic ratio represented by the region A in FIG. 61A.With such an atomic ratio, a layered structure with high carriermobility and a few grain boundaries is easily obtained.

A metal oxide with an atomic ratio in the region A, particularly in aregion B in FIG. 61B, is excellent because it easily becomes ac-axis-aligned crystalline oxide semiconductor (CAAC-OS) and has highcarrier mobility.

The CAAC-OS has c-axis alignment, its nanocrystals are connected in thea-b plane direction, and its crystal structure has distortion. Note thatthe distortion is a portion where the direction of a lattice arrangementchanges between a region with a regular lattice arrangement and anotherregion with a regular lattice arrangement in a region where nanocrystalsare connected.

The shape of the nanocrystal is basically hexagon. However, the shape isnot always a regular hexagon and is a non-regular hexagon in some cases.A pentagonal lattice arrangement, a heptagonal lattice arrangement, andthe like are sometimes included in the distortion. Note that a cleargrain boundary cannot be observed even in the vicinity of distortion inthe CAAC-OS. That is, formation of a grain boundary is inhibited by thedistortion of a lattice arrangement. This is probably because theCAAC-OS can tolerate distortion owing to a low-density arrangement ofoxygen atoms in the a-b plane direction, an interatomic bond distancechanged by substitution of a metal element, and the like.

The CAAC-OS is a metal oxide with high crystallinity. In the CAAC-OS, areduction in electron mobility due to the grain boundary is less likelyto occur because a clear grain boundary cannot be observed. Entry ofimpurities, formation of defects, or the like might decrease thecrystallinity of a metal oxide. This means that the CAAC-OS is a metaloxide having small amounts of impurities and defects (e.g., oxygenvacancies). Thus, a metal oxide including the CAAC-OS is physicallystable. Therefore, the metal oxide including the CAAC-OS is resistant toheat and has high reliability.

Note that the region B includes an atomic ratio [In]:[M]:[Zn] of 4:2:3to 4:2:4.1 and in the neighborhood thereof. The neighborhood includes anatomic ratio [In]:[M]:[Zn] of 5:3:4, for example. The region B alsoincludes an atomic ratio [In]:[M]:[Zn] of 5:1:6 and in the neighborhoodthereof and an atomic ratio [In]:[M]:[Zn] of 5:1:7 and in theneighborhood thereof.

Note that the properties of a metal oxide are not uniquely determined bythe atomic ratio. Even with the same atomic ratio, the properties of ametal oxide might differ depending on a formation condition. Forexample, when the metal oxide is formed with a sputtering apparatus, afilm having an atomic ratio deviated from the atomic ratio of a targetis formed. In particular, [Zn] in the film might be smaller than [Zn] inthe target depending on the substrate temperature in deposition. Thus,the illustrated regions each represent an atomic ratio with which ametal oxide tends to have specific properties, and boundaries of theregions A to C are not clear.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 5

In this embodiment, a CPU that can include the semiconductor device ofthe foregoing embodiment will be described.

FIG. 62 is a block diagram illustrating a configuration example of a CPUincluding the semiconductor device described in Embodiment 1.

The CPU illustrated in FIG. 62 includes, over a substrate 1190, anarithmetic logic unit (ALU) 1191, an ALU controller 1192, an instructiondecoder 1193, an interrupt controller 1194, a timing controller 1195, aregister 1196, a register controller 1197, a bus interface (bus I/F)1198, a rewritable ROM 1199, and a ROM interface (ROM I/F) 1189. Asemiconductor substrate, an SOI substrate, a glass substrate, or thelike is used as the substrate 1190. The ROM 1199 and the ROM interface1189 may be provided over a separate chip. Needless to say, the CPU inFIG. 62 is just an example with a simplified configuration, and anactual CPU has a variety of configurations depending on the application.For example, a CPU may have a GPU-like configuration where a pluralityof cores each including the CPU in FIG. 62 or an arithmetic circuitoperate in parallel. The number of bits that the CPU can handle with aninternal arithmetic circuit or a data bus can be 8, 16, 32, or 64, forexample.

An instruction that is input to the CPU through the bus interface 1198is input to the instruction decoder 1193 and decoded therein, and theninput to the ALU controller 1192, the interrupt controller 1194, theregister controller 1197, and the timing controller 1195.

The ALU controller 1192, the interrupt controller 1194, the registercontroller 1197, and the timing controller 1195 conduct various controlsin accordance with the decoded instruction. Specifically, the ALUcontroller 1192 generates signals for controlling the operation of theALU 1191. While the CPU is executing a program, the interrupt controller1194 processes an interrupt request from an external input/output deviceor a peripheral circuit depending on its priority or a mask state. Theregister controller 1197 generates an address of the register 1196, andreads/writes data from/to the register 1196 in accordance with the stateof the CPU.

The timing controller 1195 generates signals for controlling operationtimings of the ALU 1191, the ALU controller 1192, the instructiondecoder 1193, the interrupt controller 1194, and the register controller1197. For example, the timing controller 1195 includes an internal clockgenerator for generating an internal clock signal on the basis of areference clock signal, and supplies the internal clock signal to theabove circuits.

In the CPU illustrated in FIG. 62, memory cells are provided in theregister 1196. The transistor described in the foregoing embodiment canbe used in the memory cell of the register 1196.

In the CPU in FIG. 62, the register controller 1197 selects the type ofretention operation in the register 1196 in accordance with aninstruction from the ALU 1191. That is, the register controller 1197selects whether data is held by a flip-flop or by a capacitor in thememory cell included in the register 1196. When data retention by theflip-flop is selected, power supply voltage is supplied to the memorycell in the register 1196. When data retention by the capacitor isselected, the data is rewritten into the capacitor, and supply of powersupply voltage to the memory cell in the register 1196 can be stopped.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 6

The memory device of the foregoing embodiment can be used for removablememory devices such as memory cards (e.g., SD cards), universal serialbus (USB) memories, and solid state drives (SSD). In this embodiment,some structure examples of removable memory devices will be describedwith reference to FIGS. 63A to 63E.

FIG. 63A is a schematic diagram of a USB memory. A USB memory 5100includes a housing 5101, a cap 5102, a USB connector 5103, and asubstrate 5104. The substrate 5104 is held in the housing 5101. Thesubstrate 5104 is provided with a memory device and a circuit fordriving the memory device. For example, the substrate 5104 is providedwith a memory chip 5105 and a controller chip 5106. The memory cellarray 2610, the word line driver circuit 2622, the row decoder 2621, thesense amplifier 2633, the precharge circuit 2632, the column decoder2631, and the like, which are described in Embodiment 2, areincorporated into the memory chip 5105. A processor, a work memory, anECC circuit, and the like are specifically incorporated into thecontroller chip 5106. Note that the circuit configurations of the memorychip 5105 and the controller chip 5106 are not limited to thosedescribed above and can be changed as appropriate. For example, the wordline driver circuit 2622, the row decoder 2621, the sense amplifier2633, the precharge circuit 2632, and the column decoder 2631 may beincorporated into not the memory chip 5105 but the controller chip 5106.The USB connector 5103 functions as an interface for connection to anexternal device.

FIG. 63B is a schematic external diagram of an SD card, and FIG. 63C isa schematic diagram illustrating the internal structure of the SD card.An SD card 5110 includes a housing 5111, a connector 5112, and asubstrate 5113. The connector 5112 functions as an interface forconnection to an external device. The substrate 5113 is held in thehousing 5111. The substrate 5113 is provided with a memory device and acircuit for driving the memory device. For example, the substrate 5113is provided with a memory chip 5114 and a controller chip 5115. Thememory cell array 2610, the word line driver circuit 2622, the rowdecoder 2621, the sense amplifier 2633, the precharge circuit 2632, thecolumn decoder 2631, and the like, which are described in Embodiment 2,are incorporated into the memory chip 5114. A processor, a work memory,an ECC circuit, and the like are incorporated into the controller chip5115. Note that the circuit configurations of the memory chip 5114 andthe controller chip 5115 are not limited to those described above andcan be changed as appropriate. For example, the word line driver circuit2622, the row decoder 2621, the sense amplifier 2633, the prechargecircuit 2632, and the column decoder 2631 may be incorporated into notthe memory chip 5114 but the controller chip 5115.

When the memory chip 5114 is also provided on the back side of thesubstrate 5113, the capacity of the SD card 5110 can be increased. Inaddition, a wireless chip with a radio communication function may beprovided on the substrate 5113. This structure enables wirelesscommunication between an external device and the SD card 5110, making itpossible to write/read data to/from the memory chip 5114.

FIG. 63D is a schematic external diagram of an SSD, and FIG. 63E is aschematic diagram illustrating the internal structure of the SSD. An SSD5150 includes a housing 5151, a connector 5152, and a substrate 5153.The connector 5152 functions as an interface for connection to anexternal device. The substrate 5153 is held in the housing 5151. Thesubstrate 5153 is provided with a memory device and a circuit fordriving the memory device. For example, the substrate 5153 is providedwith a memory chip 5154, a memory chip 5155, and a controller chip 5156.The memory cell array 2610, the word line driver circuit 2622, the rowdecoder 2621, the sense amplifier 2633, the precharge circuit 2632, thecolumn decoder 2631, and the like, which are described in Embodiment 2,are incorporated into the memory chip 5154. When the memory chip 5154 isalso provided on the back side of the substrate 5153, the capacity ofthe SSD 5150 can be increased. A work memory is incorporated into thememory chip 5155. For example, a DRAM chip can be used as the memorychip 5155. A processor, an ECC circuit, and the like are incorporatedinto the controller chip 5156. Note that the circuit configurations ofthe memory chip 5154, the memory chip 5155, and the controller chip 5115are not limited to those described above and can be changed asappropriate. For example, a memory functioning as a work memory may alsobe provided in the controller chip 5156.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 7

This embodiment will show examples of electronic devices in which thesemiconductor device or the memory device of the foregoing embodimentcan be used.

<Laptop Personal Computer>

The semiconductor device or the memory device of one embodiment of thepresent invention can be provided in a laptop personal computer. FIG.64A illustrates a laptop personal computer including a housing 5401, adisplay portion 5402, a keyboard 5403, a pointing device 5404, and thelike.

<Smart Watch>

The semiconductor device or the memory device of one embodiment of thepresent invention can be provided in a wearable terminal. FIG. 64Billustrates a smart watch that is one of wearable terminals. The smartwatch includes a housing 5901, a display portion 5902, operation buttons5903, an operator 5904, a band 5905, and the like. A display device witha position input function may be used for the display portion 5902. Theposition input function can be added by provision of a touch panel in adisplay device. Alternatively, the position input function can be addedby provision of a photoelectric conversion element called a photosensorin a pixel area of a display device. As the operation buttons 5903, anyof a power switch for activating the smart watch, a button for operatingan application of the smart watch, a volume control button, a switch forturning on or off the display portion 5902, and the like can beprovided. Although the smart watch illustrated in FIG. 64B includes twooperation buttons 5903, the number of operation buttons included in thesmart watch is not limited to two. The operator 5904 functions as acrown used for setting the time on the smart watch. The operator 5904may be used as an input interface for operating an application of thesmart watch as well as the crown for time adjustment. Although the smartwatch in FIG. 64B includes the operator 5904, one embodiment of thepresent invention is not limited thereto and does not necessarilyinclude the operator 5904.

<Video Camera>

The semiconductor device or the memory device of one embodiment of thepresent invention can be provided in a video camera. FIG. 64Cillustrates a video camera including a first housing 5801, a secondhousing 5802, a display portion 5803, operation keys 5804, a lens 5805,a joint 5806, and the like. The operation keys 5804 and the lens 5805are provided in the first housing 5801, and the display portion 5803 isprovided in the second housing 5802. The first housing 5801 and thesecond housing 5802 are connected to each other with the joint 5806, andthe angle between the first housing 5801 and the second housing 5802 canbe changed with the joint 5806. Images displayed on the display portion5803 may be switched in accordance with the angle at the joint 5806between the first housing 5801 and the second housing 5802.

<Mobile Phone>

The semiconductor device or the memory device of one embodiment of thepresent invention can be provided in a mobile phone. FIG. 64Dillustrates a mobile phone having a function of an information terminal.The mobile phone includes a housing 5501, a display portion 5502, amicrophone 5503, a speaker 5504, and operation buttons 5505. A displaydevice with a position input function may be used for the displayportion 5502. The position input function can be added by provision of atouch panel in a display device. Alternatively, the position inputfunction can be added by provision of a photoelectric conversion elementcalled a photosensor in a pixel area of a display device. As theoperation buttons 5505, any of a power switch for activating the mobilephone, a button for operating an application of the mobile phone, avolume control button, a switch for turning on or off the displayportion 5502, and the like can be provided.

Although the mobile phone illustrated in FIG. 64D includes two operationbuttons 5505, the number of operation buttons included in the mobilephone is not limited to two. Although not illustrated, the mobile phonein FIG. 64D may include a light-emitting device used for a flashlight ora lighting purpose.

<Television Device>

The semiconductor device or the memory device of one embodiment of thepresent invention can be provided in a television device. FIG. 64E is aperspective view illustrating a television device. The television deviceincludes a housing 9000, a display portion 9001, a speaker 9003, anoperation key 9005 (including a power switch or an operation switch), aconnection terminal 9006, a sensor 9007 (a sensor having a function ofmeasuring force, displacement, position, speed, acceleration, angularvelocity, rotational frequency, distance, light, liquid, magnetism,temperature, chemical substance, sound, time, hardness, electric field,current, voltage, power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), and the like. The televisiondevice can include the display portion 9001 of 50 inches or more or 100inches or more, for example.

<Vehicle>

The semiconductor device or the memory device of one embodiment of thepresent invention can also be used around a driver's seat in a car,which is a vehicle.

As an example, FIG. 64F illustrates a front glass and its vicinityinside a car. FIG. 64F shows a display panel 5701, a display panel 5702,and a display panel 5703 that are attached to a dashboard and a displaypanel 5704 that is attached to a pillar.

The display panels 5701 to 5703 can provide a variety of kinds ofinformation such as navigation information, a speedometer, a tachometer,a mileage, a fuel meter, a gearshift indicator, and air-conditionsetting. Items shown on the display panel, their layout, and the likecan be changed as appropriate to suit the user's preferences, resultingin more sophisticated design. The display panels 5701 to 5703 can alsobe used as lighting devices.

The display panel 5704 can compensate for the view obstructed by thepillar (blind areas) by showing an image taken by an imaging unitprovided for the car body. That is, displaying an image taken by theimaging unit provided on the outside of the car body leads toelimination of blind areas and enhancement of safety. Moreover, showingan image to compensate for the area that a driver cannot see makes itpossible for the driver to confirm safety more easily and comfortably.The display panel 5704 can also be used as a lighting device.

The semiconductor device or the memory device of one embodiment of thepresent invention can be used, for example, for a frame memory thattemporarily stores image data used to display images on the displaypanels 5701 to 5704, or a memory device that stores a program fordriving a system included in the vehicle.

Although not shown, each of the electronic devices illustrated in FIGS.64A, 64B, 64E, and 64F may include a microphone and a speaker. Theelectronic device with this structure can have an audio input function,for example.

Although not shown, each of the electronic devices illustrated in FIGS.64A, 64B, 64D, 64E, and 64F may include a camera.

Although not illustrated, each of the electronic devices in FIGS. 64A to64F may include a sensor (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays) in the housing. In particular, whenthe mobile phone in FIG. 64D is provided with a sensing device thatincludes a sensor for sensing inclination, such as a gyroscope sensor oran acceleration sensor, the orientation of the mobile phone (withrespect to the vertical direction) can be determined to change thedisplay on the screen of the display portion 5502 automatically inaccordance with the orientation of the mobile phone.

Although not illustrated, each of the electronic devices in FIGS. 64A to64F may include a device for obtaining biological information such asfingerprints, veins, iris, or voice prints. The electronic device withthis structure can have a biometric identification function.

A flexible base may be used for the display portion of each of theelectronic devices in FIGS. 64A to 64F. Specifically, the displayportion may have a structure in which a transistor, a capacitor, adisplay element, and the like are provided over a flexible base. Withsuch a structure, in addition to the electronic device having thehousing with a flat surface as illustrated in FIGS. 64A to 64F, anelectronic device having a housing with a curved surface can beachieved.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

(Notes on Description of this Specification and the Like)

The following are notes on the structures in the above embodiments.

<Notes on One Embodiment of the Present Invention Described inEmbodiments>

One embodiment of the present invention can be constituted byappropriately combining the structure described in an embodiment withany of the structures described in the other embodiments. In the casewhere a plurality of structure examples are described in one embodiment,some of the structure examples can be combined as appropriate.

Note that a content (or part thereof) described in one embodiment can beapplied to, combined with, or replaced with another content (or partthereof) described in the same embodiment and/or a content (or partthereof) described in another embodiment or other embodiments.

Note that in each embodiment, a content described in the embodiment is acontent described with reference to a variety of diagrams or a contentdescribed with text disclosed in this specification.

By combining a diagram (or part thereof) described in one embodimentwith another part of the diagram, a different diagram (or part thereof)described in the embodiment, and/or a diagram (or part thereof)described in another embodiment or other embodiments, much more diagramscan be created.

<Notes on Ordinal Numbers>

In this specification and the like, ordinal numbers such as first,second, and third are used in order to avoid confusion among components.Thus, the terms do not limit the number or order of components. In thisspecification and the like, for example, a “first” component in oneembodiment can be referred to as a “second” component or omitted inother embodiments or claims.

<Notes on Description for Drawings>

The embodiments are described with reference to the drawings. Note thatthe embodiments can be implemented in many different modes, and it willbe readily appreciated by those skilled in the art that modes anddetails can be changed in various ways without departing from the spiritand scope of the present invention. Thus, the present invention shouldnot be interpreted as being limited to the description of theembodiments. Note that in the structures of the invention described inEmbodiments, the same portions or portions having similar functions aredenoted by the same reference numerals in different drawings, and thedescription of such portions is not repeated.

In this specification and the like, terms for explaining arrangement(e.g., over, above, under, and below) are used for convenience toindicate a positional relation between components with reference todrawings. The positional relation between components is changed asappropriate in accordance with a direction in which the components aredescribed. Therefore, the terms for explaining arrangement are notlimited to those used in the specification and the like, and can bechanged to other terms as appropriate depending on the situation. Forexample, the expression “an insulator over (on) a top surface of aconductor” can be replaced with the expression “an insulator on a bottomsurface of a conductor” when the direction of a diagram showing thesecomponents is rotated by 180°.

The term such as “over,” “above, “under,” and “below” does notnecessarily mean that a component is placed directly on or under anddirectly in contact with another component. For example, the expression“electrode B over insulating layer A” does not necessarily mean that theelectrode B is on and in direct contact with the insulating layer A andcan also mean the case where another component is provided between theinsulating layer A and the electrode B.

In the drawings, the size, the layer thickness, or the region isdetermined arbitrarily for description convenience; therefore,embodiments of the present invention are not limited to the illustratedscale. Note that the drawings are schematically shown for clarity, andembodiments of the present invention are not limited to shapes or valuesshown in the drawings. For example, the following can be included:variation in signal, voltage, or current due to noise or difference intiming.

In drawings such as perspective views, some of components might not beillustrated for clarity of the drawings.

In the drawings, the same components, components having similarfunctions, components formed of the same material, or components formedat the same time are sometimes denoted by the same reference numerals,and the description thereof is not repeated in some cases.

<Notes on Expressions that can be Rephrased>

In this specification and the like, the terms “one of a source and adrain” (or a first electrode or a first terminal) and “the other of thesource and the drain” (or a second electrode or a second terminal) areused to describe the connection relation of a transistor. This isbecause the source and the drain of a transistor are interchangeabledepending on the structure, operation conditions, or the like of thetransistor. Note that the source or the drain of the transistor can alsobe referred to as a source (or drain) terminal, a source (or drain)electrode, or the like as appropriate depending on the situation. Inthis specification and the like, two terminals except a gate aresometimes referred to as a first terminal and a second terminal or as athird terminal and a fourth terminal. In this specification and thelike, a channel formation region refers to a region where a channel isformed; the formation of this region by application of a potential tothe gate enables current to flow between the source and the drain.

Functions of a source and a drain are sometimes switched when atransistor of different polarity is employed or when a direction ofcurrent flow is changed in circuit operation, for example. Therefore,the terms “source” and “drain” can be used interchangeably in thisspecification and the like.

In this specification and the like, in the case where a transistor hastwo or more gates (such a structure is sometimes referred to as adual-gate structure), these gates are referred to as a first gate and asecond gate or as a front gate and a backgate in some cases. Inparticular, the term “front gate” can be replaced with a simple term“gate.” The term “backgate” can be replaced with a simple term “gate.”Note that a bottom gate is a terminal that is formed before a channelformation region in manufacture of a transistor, and a top gate is aterminal that is formed after a channel formation region in manufactureof a transistor.

In this specification and the like, the term such as “electrode” or“wiring” does not limit a function of a component. For example, an“electrode” is used as part of a “wiring” in some cases, and vice versa.Moreover, the term “electrode” or “wiring” can also mean a combinationof a plurality of electrodes or wirings formed in an integrated manner.

In this specification and the like, “voltage” and “potential” can bereplaced with each other. The term “voltage” refers to a potentialdifference from a reference potential. When the reference potential is aground potential, for example, “voltage” can be replaced with“potential.” A ground potential does not necessarily mean 0 V.Potentials are relative values, and a potential supplied to a wiring orthe like is sometimes changed depending on the reference potential.

In this specification and the like, the terms “film” and “layer” can beinterchanged with each other depending on the case or circumstances. Forexample, in some cases, the term “conductive film” can be used insteadof “conductive layer,” and the term “insulating layer” can be usedinstead of “insulating film.” Moreover, such terms can be replaced witha word not including the term “film” or “layer” depending on the case orcircumstances. For example, in some cases, the term “conductor” can beused instead of “conductive layer” or “conductive film,” and the term“insulator” can be used instead of “insulating layer” or “insulatingfilm.”

In this specification and the like, the terms “wiring,” “signal line,”“power supply line,” and the like can be replaced with each otherdepending on the case or circumstances. For example, in some cases, theterm “signal line” or “power supply line” can be used instead of“wiring,” and vice versa. In some cases, the term “signal line” can beused instead of “power supply line,” and vice versa. As another example,the term “signal” can be used instead of “potential” that is supplied toa wiring and vice versa, depending on the case or circumstances.

<Notes on Definitions of Terms>

The following are definitions of the terms mentioned in the aboveembodiments.

<<Impurities in Semiconductor>>

Impurities in a semiconductor refer to, for example, elements other thanthe main components of a semiconductor layer. For instance, an elementwith a concentration of lower than 0.1 atomic % is an impurity. Ifimpurities are contained in a semiconductor, the density of states (DOS)may be formed in the semiconductor, the carrier mobility may bedecreased, or the crystallinity may be decreased, for example. When thesemiconductor is an oxide semiconductor, examples of impurities thatchange characteristics of the semiconductor include Group 1 elements,Group 2 elements, Group 13 elements, Group 14 elements, Group 15elements, and transition metals other than the main components of thesemiconductor. Specific examples are hydrogen (included also in water),lithium, sodium, silicon, boron, phosphorus, carbon, and nitrogen. Whenthe semiconductor is an oxide semiconductor, oxygen vacancies may beformed by entry of impurities such as hydrogen, for instance. When thesemiconductor is silicon, examples of impurities that change thecharacteristics of the semiconductor include oxygen, Group 1 elementsexcept hydrogen, Group 2 elements, Group 13 elements, and Group 15elements.

<<Switch>>

In this specification and the like, a switch is conducting or notconducting (is turned on or off) to determine whether current flowstherethrough or not. Alternatively, a switch has a function of selectingand changing a current path.

For example, an electrical switch or a mechanical switch can be used.That is, a switch is not limited to a certain element and can be anyelement capable of controlling current.

Examples of an electrical switch include a transistor (e.g., a bipolartransistor and a MOS transistor), a diode (e.g., a PN diode, a PINdiode, a Schottky diode, a metal-insulator-metal (MIM) diode, ametal-insulator-semiconductor (MIS) diode, and a diode-connectedtransistor), and a logic circuit in which such elements are combined.

In the case of using a transistor as a switch, the on state of thetransistor refers to a state in which a source electrode and a drainelectrode of the transistor are regarded as being electricallyshort-circuited. The off state of the transistor refers to a state inwhich the source electrode and the drain electrode of the transistor areregarded as being electrically disconnected. In the case where atransistor operates just as a switch, there is no particular limitationon the polarity (conductivity type) of the transistor.

An example of a mechanical switch is a switch using amicroelectromechanical systems (MEMS) technology, such as a digitalmicromirror device (DMD). Such a switch includes an electrode that canbe moved mechanically, and its conduction and non-conduction iscontrolled with movement of the electrode.

<<Connection>>

In this specification and the like, the description “X and Y areconnected” means that X and Y are electrically connected, X and Y arefunctionally connected, and X and Y are directly connected. Accordingly,without being limited to a predetermined connection relation (e.g., aconnection relation shown in drawings and texts), another connectionrelation is regarded as being included in the drawings and the texts.

Here, X and Y each denote an object (e.g., a device, an element, acircuit, a wiring, an electrode, a terminal, a conductive film, or alayer).

For example, in the case where X and Y are electrically connected, atleast element that enables electrical connection between X and Y (e.g.,a switch, a transistor, a capacitor, an inductor, a resistor, a diode, adisplay element, a light-emitting element, or a load) can be connectedbetween X and Y. Note that a switch is controlled to be turned on oroff. That is, a switch is conducting or not conducting (is turned on oroff) to determine whether current flows therethrough or not.

For example, in the case where X and Y are functionally connected, atleast one circuit that enables functional connection between X and Y(e.g., a logic circuit such as an inverter, a NAND circuit, or a NORcircuit; a signal converter circuit such as a DA converter circuit, anAD converter circuit, or a gamma correction circuit; a potential levelconverter circuit such as a power supply circuit (e.g., a step-upcircuit or a step-down circuit) or a level shifter circuit for changingthe potential level of a signal; a voltage source; a current source; aswitching circuit; an amplifier circuit such as a circuit capable ofincreasing signal amplitude, the amount of current, or the like, anoperational amplifier, a differential amplifier circuit, a sourcefollower circuit, or a buffer circuit; a signal generator circuit; amemory circuit; and/or a control circuit) can be connected between X andY. For instance, even if another circuit is provided between X and Y, Xand Y are regarded as being functionally connected when a signal outputfrom X is transmitted to Y.

Note that an explicit description “X and Y are electrically connected”means that X and Y are electrically connected (i.e., X and Y areconnected with another element or circuit provided therebetween), X andY are functionally connected (i.e., X and Y are functionally connectedwith another circuit provided therebetween), and X and Y are directlyconnected (i.e., X and Y are connected without another element orcircuit provided therebetween). That is, the term “electricallyconnected” is substantially the same as the term “connected.”

For example, any of the following expressions can be used for the casewhere a source (or a first terminal or the like) of a transistor iselectrically connected to X through (or not through) Z1 and a drain (ora second terminal or the like) of the transistor is electricallyconnected to Y through (or not through) Z2, or the case where a source(or a first terminal or the like) of a transistor is directly connectedto one part of Z1 and another part of Z1 is directly connected to Xwhile a drain (or a second terminal or the like) of the transistor isdirectly connected to one part of Z2 and another part of Z2 is directlyconnected to Y.

Examples of the expressions include “X, Y, and a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor are electrically connected to each other, and X, the source(or the first terminal or the like) of the transistor, the drain (or thesecond terminal or the like) of the transistor, and Y are electricallyconnected in this order,” “a source (or a first terminal or the like) ofa transistor is electrically connected to X, a drain (or a secondterminal or the like) of the transistor is electrically connected to Y,and X, the source (or the first terminal or the like) of the transistor,the drain (or the second terminal or the like) of the transistor, and Yare electrically connected in this order,” and “X is electricallyconnected to Y through a source (or a first terminal or the like) and adrain (or a second terminal or the like) of a transistor, and X, thesource (or the first terminal or the like) of the transistor, the drain(or the second terminal or the like) of the transistor, and Y areprovided to be connected in this order.” When the connection order in acircuit configuration is defined by an expression similar to the aboveexamples, a source (or a first terminal or the like) and a drain (or asecond terminal or the like) of a transistor can be distinguished fromeach other to specify the technical scope. Note that the aboveexpressions are examples, and there is no limitation on the expressions.Here, X, Y, Z1, and Z2 each denote an object (e.g., a device, anelement, a circuit, a wiring, an electrode, a terminal, a conductivefilm, or a layer).

Even when a circuit diagram shows that independent components areelectrically connected to each other, one component sometimes hasfunctions of a plurality of components. For example, when part of awiring also functions as an electrode, one conductive film functions asthe wiring and the electrode. Thus, the term “electrical connection” inthis specification also means such a case where one conductive film hasfunctions of a plurality of components.

<<Parallel and Perpendicular>>

In this specification, the term “parallel” indicates that the angleformed between two straight lines ranges from −10° to 10°, andaccordingly also includes the case where the angle ranges from −5° to5°. The term “substantially parallel” indicates that the angle formedbetween two straight lines ranges from −30° to 30°. The term“perpendicular” indicates that the angle formed between two straightlines ranges from 80° to 100°, and accordingly also includes the casewhere the angle ranges from 85° to 95°. The term “substantiallyperpendicular” indicates that the angle formed between two straightlines ranges from 60° to 120°.

This application is based on Japanese Patent Application Serial No.2017-141515 filed with Japan Patent Office on Jul. 21, 2017, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a firstinsulator, a second insulator, a third insulator, a fourth insulator, afifth insulator, a sixth insulator, a seventh insulator, a firstconductor, a second conductor, a first semiconductor, and a secondsemiconductor, wherein: the first conductor is positioned on a first topsurface of the first insulator and on a first bottom surface of thesecond insulator, the second conductor is positioned on a top surface ofthe second insulator and on a bottom surface of the third insulator, thefourth insulator is positioned in a region comprising a side surface ofthe first insulator, a second top surface of the first insulator, a sidesurface of the first conductor, a second bottom surface of the secondinsulator, a side surface of the second insulator, a side surface of thesecond conductor and a side surface of the third insulator, the firstsemiconductor is in contact with the fourth insulator, the fifthinsulator is in contact with the first semiconductor in a regionoverlapping the first conductor with the fourth insulator positionedbetween the first semiconductor and the first conductor, the sixthinsulator is positioned in a region comprising: the first semiconductorin a region overlapping the first insulator, in a region overlapping thesecond insulator, in a region overlapping the second conductor, in aregion overlapping the third insulator; and the fifth insulator, thesecond semiconductor is in contact with the sixth insulator, and theseventh insulator is in contact with the second semiconductor.
 2. Thesemiconductor device according to claim 1, further comprising a thirdconductor in contact with the seventh insulator.
 3. The semiconductordevice according to claim 1, wherein the first semiconductor comprises alow-resistance region at and around an interface with the sixthinsulator, and wherein the first semiconductor comprises a channelformation region in a region overlapping the first conductor.
 4. Thesemiconductor device according to claim 3, wherein the firstsemiconductor comprises a metal oxide, wherein the low-resistance regioncomprises a conductive compound, and wherein the conductive compoundcomprises a component identical to a component included in the metaloxide and a component identical to a component included in the sixthinsulator.
 5. The semiconductor device according to claim 3, wherein thefirst semiconductor comprises a metal oxide, wherein the low-resistanceregion comprises a conductive compound, and wherein the conductivecompound comprises a component identical to a component included in themetal oxide, and a metal element.
 6. A semiconductor wafer comprising: aplurality of the semiconductor devices according to claim 1; and aregion to be subjected to dicing.
 7. A memory device comprising: thesemiconductor device according to claim 1; and a peripheral circuit. 8.An electronic device comprising: the memory device according to claim 7;and a housing.